UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.    )

Filed by the Registrant  ☑                             Filed by a Party other than the Registrant  ☐

Check the appropriate box:

WILLIS TOWERS WATSON PUBLIC LIMITED COMPANY

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check the appropriate box):

Willis Towers Watson Public Limited Company

Willis Towers Watson House, Elm Park,

Merrion Road, Dublin 4 Ireland

TRANSACTION PROPOSED—YOUR VOTE IS VERY IMPORTANT

To our Shareholders:

You are cordially invited to attend two special meetings of the shareholders of Willis Towers Watson Public Limited Company, an Irish public limited company, referred to as “WTW.” The first, the special Court-ordered meeting of shareholders, referred to as the “WTW Court Meeting,” is to be held on August 26, 2020 at 10:30 a.m., EDT, and the second, the extraordinary general meeting of shareholders, referred to as the “WTW EGM,” is to be held on August 26, 2020 at 11:00 a.m., EDT, or, if the WTW Court Meeting has not concluded by 11:00 a.m., EDT, as soon as possible after the conclusion or adjournment of the WTW Court Meeting. Both the WTW Court Meeting and the WTW EGM will be held at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States and Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland (where such participation in Ireland shall be by technological means) and shall constitute, in the case of attendance in either of such locations, being present in person at the WTW Court Meeting or the WTW EGM, as the case may be.

As previously announced, on March 9, 2020, WTW and Aon plc, a public limited company incorporated in England, referred to as “Aon UK,” entered into a Business Combination Agreement, referred to as the “Business Combination Agreement,” providing for the combination of the two companies. On April 1, 2020, Aon UK completed its previously announced cancellation scheme of arrangement, pursuant to which an Irish public limited company named Aon plc, referred to as “Aon Ireland,” became the public parent company of Aon UK, and all of the members of the board of directors of Aon UK became members of the board of directors of Aon Ireland. In connection with the foregoing, on April 2, 2020, Aon UK assigned all of its rights and obligations under the Business Combination Agreement to Aon Ireland, and Aon Ireland assumed all such rights and obligations. We refer to Aon UK, prior to such assignment, and Aon Ireland, after such assignment, as “Aon.”

Under the terms of the Business Combination Agreement, Aon has agreed to acquire the entire issued ordinary share capital of WTW, which acquisition, referred to as the “transaction,” is to be implemented by way of a court-sanctioned scheme of arrangement, referred to as the “scheme,” to be undertaken by WTW under Chapter 1, Part 9 of the Irish Companies Act 2014. If the transaction is completed, WTW shareholders will be entitled to receive, at the effective time of the scheme, referred to as the “effective time,” 1.08 Class A ordinary shares, nominal value $0.01 per share, of Aon, referred to as the “Aon Shares,” for each Class A ordinary share, nominal value $0.000304635 per share, of WTW, referred to as the “WTW Shares,” owned by such WTW shareholders and subject to the scheme. As a result of the scheme, WTW will become a wholly-owned subsidiary of Aon. Following the closing of the transaction, referred to as the “closing,” it is anticipated that the shareholders of Aon and WTW immediately prior to the closing will own approximately 62.8% and 37.2% of the combined company immediately following the closing, respectively, based on the number of Aon Shares and WTW Shares outstanding as of June 30, 2020 on a fully diluted basis.

WTW equity awards will be treated as set forth in the Business Combination Agreement, such that, as of immediately prior to the effective time, (i) each WTW share option and restricted share unit award (other than any WTW restricted share unit award granted to a WTW non-employee director) that is outstanding immediately prior to the effective time will be converted into a corresponding award relating to Aon Shares, with the number of Aon Shares subject to such award and, if applicable, the exercise price applicable to such award, determined in accordance with the formulas set forth in the Business Combination Agreement, and (ii) each WTW performance share unit award and phantom share unit award that is outstanding immediately prior to the effective time will be converted into a corresponding award that vests based on the holder’s continued service following the effective time and relates to a number of Aon Shares determined in accordance with the formulas set forth in the Business Combination Agreement. Immediately prior to the effective time, each WTW restricted share unit award granted

to a WTW non-employee director will vest and thereafter be settled in Aon Shares. For a description of the treatment of WTW equity awards, see the section entitled “The Business Combination Agreement—Treatment of WTW Equity Awards” beginning on page 131 of the accompanying joint proxy statement.

You are being asked to vote on a proposal to approve the scheme at both special meetings, as well as certain additional proposals being presented at the WTW EGM that shareholders must approve in order to properly implement the scheme and consummate the transaction. The scheme is also subject to approval by the Irish High Court. More information about the transaction and the proposals for which your approval is being sought is contained in the accompanying joint proxy statement. We urge all WTW shareholders to read the accompanying joint proxy statement, including the annexes and the documents incorporated by reference therein, carefully and in their entirety. In particular, we urge you to read carefully the section entitled “Risk Factors” beginning on page 35 of the accompanying joint proxy statement.

Your proxy is being solicited by the members of the board of directors of WTW, referred to as the “WTW Board.” After careful consideration, the members of the WTW Board have unanimously determined that the Business Combination Agreement and the transactions contemplated thereby, including the scheme, are fair and reasonable. The WTW Board recommends unanimously that you vote “FOR” all proposals being presented at the special meetings. In considering the recommendation of the WTW Board, you should be aware that certain WTW directors and executive officers have interests in the transaction that are in addition to, or different from, the interests they might have as WTW shareholders generally. See the section entitled “The Transaction—Interests of WTW Directors and Executive Officers in the Transaction” beginning on page 109 of the accompanying joint proxy statement for more information. Your vote is very important, regardless of the number of shares you own. Please vote as soon as possible, whether or not you plan to attend the special meetings, by following the instructions in the accompanying joint proxy statement.

Irish law requires WTW to hold a physical meeting for the WTW Court Meeting and the WTW EGM. In light of COVID-19, we encourage WTW shareholders to vote by proxy prior to 11:59 p.m. EDT on August 25, 2020 as described in the accompanying joint proxy statement. WTW asks that, in considering whether to attend such meetings in person, WTW shareholders follow public health and travel guidelines with respect to COVID-19, including as applicable to Ireland and the United States. Those guidelines may restrict or prevent any WTW shareholder from attending such meetings in person. WTW strongly encourages WTW shareholders not to attend such meetings in person if they are experiencing any of the described COVID-19 symptoms. WTW shareholders attending the WTW special meetings in person are also requested to follow the hygiene instructions consistent with applicable public health guidelines, including washing or disinfecting hands upon arrival at such meetings. WTW may take additional precautionary measures in relation to the WTW special meetings in response to further developments in the COVID-19 outbreak. WTW will be obliged to comply with any legal restrictions that are imposed as a consequence of COVID-19 and that affect such meetings, which may include preventing or restricting access to such meetings. WTW also intends to comply with any applicable public health and travel guidelines, which may affect the WTW special meetings. Depending on concerns about and developments relating to the COVID-19 outbreak, the WTW Board could determine to change the date, time, location or format of the WTW special meetings, subject to Irish legal requirements. In the event WTW determines it is necessary or appropriate to take additional steps regarding how the WTW special meetings will be conducted, WTW will announce such determinations in advance in accordance with applicable legal requirements, and details will be posted on WTW’s website and filed with the U.S. Securities and Exchange Commission.

On behalf of the WTW Board, thank you for your consideration and continued support.

Very truly yours,

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued in connection with the transaction or determined if the accompanying joint proxy statement is accurate or complete. Any representation to the contrary is a criminal offense.

For the avoidance of doubt, the accompanying joint proxy statement is not intended to be and is not a prospectus for the purposes of the Irish Companies Act 2014, Regulation (EU) 2017/1129, the European Union (Prospectus) Regulations 2019 or the Central Bank (Investment Market Conduct) Rules 2019, and the Central Bank of Ireland has not approved this document.

The accompanying joint proxy statement is dated as of July 8, 2020, and is first being mailed to WTW shareholders on or about July 8, 2020.

Aon plc

Metropolitan Building

James Joyce Street, Dublin 1, Ireland D01 K0Y8

TRANSACTION PROPOSED—YOUR VOTE IS VERY IMPORTANT

Dear Aon shareholder:

You are cordially invited to an extraordinary general meeting of shareholders of Aon plc, referred to as the “Aon EGM” which will be held on August 26, 2020 at 10:00 a.m., CDT (11:00 a.m., EDT), at 200 East Randolph Street, Chicago, Illinois 60601, United States and, at the same time, Arthur Cox, Ten Earlsfort Terrace, Dublin 2, D02 T380, Ireland (where such participation in Ireland shall be by technological means).

As previously announced, on March 9, 2020, Aon plc, a public limited company incorporated in England, referred to as “Aon UK,” and Willis Towers Watson Public Limited Company, an Irish public limited company, referred to as “WTW,” entered into a Business Combination Agreement, referred to as the “Business Combination Agreement,” providing for the combination of the two companies. On April 1, 2020, Aon UK completed its previously announced cancellation scheme of arrangement, pursuant to which an Irish public limited company named Aon plc, referred to as “Aon Ireland,” became the public parent company of Aon UK, and all of the members of the board of directors of Aon UK became members of the board of directors of Aon Ireland. In connection with the foregoing, on April 2, 2020, Aon UK assigned all of its rights and obligations under the Business Combination Agreement to Aon Ireland, and Aon Ireland assumed all such rights and obligations. We refer to Aon UK, prior to such assignment, and Aon Ireland, after such assignment, as “Aon.”

Under the terms of the Business Combination Agreement, Aon is to acquire WTW pursuant to a scheme of arrangement, referred to as the “scheme,” under Chapter 1 of Part 9 of the Irish Companies Act 2014, subject to the approval of the scheme by the Irish High Court. If the transaction is completed, WTW shareholders will be entitled to receive, at the effective time of the scheme, referred to as the “effective time,” 1.08 newly issued Class A ordinary shares of Aon, referred to as “Aon Shares,” in exchange for each ordinary share of WTW owned by such WTW shareholders and subject to the scheme. As a result of the scheme, WTW will become a wholly-owned subsidiary of Aon. Following the closing of the transaction, referred to as the “closing,” it is anticipated that the shareholders of Aon and WTW immediately prior to the closing will own approximately 62.8% and 37.2% of the combined company immediately following the closing, respectively, based on the number of Aon Shares and WTW Shares outstanding as of June 30, 2020 on a fully diluted basis.

WTW equity awards will be treated as set forth in the Business Combination Agreement, such that, as of immediately prior to the effective time, (i) each WTW share option and restricted share unit award (other than any WTW restricted share unit award granted to a WTW non-employee director) that is outstanding immediately prior to the effective time will be converted into a corresponding award relating to Aon Shares, with the number of Aon Shares subject to such award and, if applicable, the exercise price applicable to such award, determined in accordance with the formulas set forth in the Business Combination Agreement, and (ii) each WTW performance share unit award and phantom share unit award that is outstanding immediately prior to the effective time will be converted into a corresponding award that vests based on the holder’s continued service following the effective time and relates to a number of Aon Shares determined in accordance with the formulas set forth in the Business Combination Agreement. Immediately prior to the effective time, each WTW restricted share unit award granted to a WTW non-employee director will vest and thereafter be settled in Aon Shares. For a description of the treatment of WTW equity awards, see the section entitled “The Business Combination Agreement—Treatment of WTW Equity Awards” beginning on page 131 of the accompanying joint proxy statement.

At the Aon EGM, you are being asked to vote on a proposal to approve the issuance of the aggregate scheme consideration pursuant to the transaction, as well as certain related proposals. More information about the transaction and the other proposals is contained in the accompanying joint proxy statement. We urge all Aon shareholders to read the accompanying joint proxy statement, including the annexes thereto and the documents incorporated by reference therein, carefully and in their entirety. In particular, we urge you to carefully read the section entitled “Risk Factors” beginning on page 35 of the accompanying joint proxy statement.

Your proxy is being solicited by the members of Aon’s board of directors, referred to as the “Aon Board,” entitled to solicit your proxy.

After careful consideration, the members of the Aon Board have unanimously approved the Business Combination Agreement and determined that the terms of the transaction are fair to and in the best interests of Aon and its shareholders. The Aon Board unanimously recommends that you vote “FOR” all proposals being presented at the Aon EGM. In considering the recommendation of the Aon Board, you should be aware that certain Aon directors and executive officers have interests in the transaction that are in addition to, or different from, the interests they might have as Aon shareholders generally. See the section entitled “The Transaction—Interests of Aon Directors and Executive Officers in the Transaction” beginning on page 115 of the accompanying joint proxy statement for more information. Your vote is very important, regardless of the number of shares you own. Please vote as soon as possible by following the instructions in the accompanying joint proxy statement.

As part of our precautions regarding the recent outbreak of COVID-19, we are sensitive to the public health and travel concerns that Aon shareholders may have, as well as any protocols that governmental entities may impose. Accordingly, we have made arrangements to enable persons to attend the Aon EGM virtually via the internet. The virtual attendance does not extend to voting at the Aon EGM. Irish law requires Aon to hold a physical meeting for the Aon EGM. In light of COVID-19, we strongly encourage Aon shareholders not to attend the Aon EGM in person, but to vote their Aon Shares in advance via the internet, by telephone, or by completing, signing and returning a form of proxy or voting instruction form, in each case as described in the accompanying joint proxy statement and, if you wish to hear the proceedings and ask questions, to do so virtually as described in the accompanying proxy statement. Aon asks that, in considering whether to attend the Aon EGM in person, Aon shareholders follow public health and travel guidelines with respect to COVID-19, including as applicable to Ireland and the United States. Those guidelines may restrict or prevent any Aon shareholder from attending the Aon EGM in person. Aon shareholders attending the Aon EGM in person are also requested to follow the hygiene instructions consistent with applicable public health guidelines, including washing or disinfecting hands upon arrival at the Aon EGM. Aon may take additional precautionary measures in relation to the Aon EGM in response to further developments in the COVID-19 outbreak. Aon will be obliged to comply with any applicable legal restrictions that are imposed as a consequence of COVID-19 and that affect the Aon EGM, which may include preventing or restricting access to the Aon EGM. Aon also intends to comply with any public health and travel guidelines, which may affect the Aon EGM. Depending on concerns about and developments relating to the COVID-19 outbreak, the board of directors of Aon could determine to change the date, time, location or format of the Aon EGM, subject to Irish legal requirements. In the event Aon determines it is necessary or appropriate to take additional steps regarding how the Aon EGM will be conducted, we will announce such determinations in advance in accordance with applicable legal requirements, and details will be posted on our website and filed with the U.S. Securities and Exchange Commission.

On behalf of the Aon Board, thank you for your consideration and continued support.

Very truly yours,

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued in connection with the transaction or determined if the accompanying joint proxy statement is accurate or complete. Any representation to the contrary is a criminal offense.

For the avoidance of doubt, the accompanying joint proxy statement is not intended to be and is not a prospectus for the purposes of the Irish Companies Act 2014, Regulation (EU) 2017/1129, the European Union (Prospectus) Regulations 2019 or the Central Bank (Investment Market Conduct) Rules 2019, and the Central Bank of Ireland has not approved this document.

The accompanying joint proxy statement is dated as of July 8, 2020, and is first being mailed to Aon shareholders on or about, July 8, 2020.

WILLIS TOWERS WATSON PLC

Willis Towers Watson House, Elm Park,

Merrion Road, Dublin 4, Ireland

NOTICE OF COURT MEETING OF SHAREHOLDERS

THE HIGH COURT, 2020 No. 2020 / 198 COS

IN THE MATTER OF WILLIS TOWERS WATSON PLC

– and –

IN THE MATTER OF THE COMPANIES ACT 2014

NOTICE IS HEREBY GIVEN that by a Court Order dated July 6, 2020, made in the above matters, the High Court of Ireland, referred to as the “Irish High Court,” has directed a meeting, referred to as the “WTW Court Meeting” to be convened of the holders of the Scheme Shares (as defined in the proposed scheme of arrangement that is included in the document of which this Notice forms a part) of Willis Towers Watson Public Limited Company, referred to as “WTW,” for the purpose of considering and, if thought fit, approving a resolution to approve (with or without modification) a scheme of arrangement pursuant to Chapter 1 of Part 9 of the Companies Act 2014 proposed to be made between WTW and the holders of the Scheme Shares, referred to as the “scheme” or “scheme of arrangement” (and that such meeting will be held at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States, and Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland (where such participation in Ireland shall be by technological means) and shall constitute, in the case of attendance in either of such locations in the United States or Ireland, being present in person at the WTW Court Meeting), on August 26, 2020, at 10:30 a.m., EDT, at which place and time all holders of the Scheme Shares entitled to vote thereat are invited to attend; such resolution being in the following terms:

“That the scheme in its original form or with or subject to any modification(s), addition(s) or condition(s) approved or imposed by the Irish High Court be agreed to.”

A copy of the scheme of arrangement and a copy of the explanatory statement required to be furnished pursuant to Section 452 of the Companies Act 2014 are included in the document of which this Notice forms a part.

Scheme Shareholders (as defined in the scheme of arrangement that is included in the document of which this Notice forms a part) may vote in person at the WTW Court Meeting or they may appoint another person, whether a member of WTW or not, as their proxy to attend, speak and vote in their stead. The WTW Court Meeting will be held at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States and Scheme Shareholders (or their proxies) may also participate (by technological means) in the WTW Court Meeting in Ireland at Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland, at the time of the WTW Court Meeting (and such participation shall constitute presence in person at the WTW Court Meeting). A form of proxy for use at the WTW Court Meeting is enclosed with this Notice. Completion and return of a form of proxy will not preclude a Scheme Shareholder from attending and voting in person at the WTW Court Meeting, or any adjournment thereof, if that shareholder wishes to do so. Any alteration to the form of proxy must be initialed by the person who signs it.

It is requested that a form of proxy, duly completed and signed, together with any power of attorney, under which it is signed, be submitted by following the instructions set forth on the proxy card no later than 11:59 p.m. EDT on August 25, 2020 but, if a form of proxy is not so submitted, it may be handed to the chairman of the WTW Court Meeting in Miami or to a representative of Matheson, legal advisors to WTW, in Dublin before the start of the WTW Court Meeting and will still be valid.

Scheme Shareholders may also submit a proxy or proxies via the internet by accessing the website www.proxyvote.com or vote by telephone by calling the toll-free telephone number listed on the voter instruction form or proxy card anytime up to 11:59 p.m. EDT on August 25, 2020. All proxies will be forwarded to WTW electronically.

In the case of joint holders, the vote of the senior member who tenders a vote, whether in person or by proxy, will be accepted to the exclusion of the vote(s) of the other joint holder(s) and, for this purpose, seniority will be determined by the order in which the names stand in WTW’s register of members in respect of the joint holding.

Entitlement to attend and vote at the WTW Court Meeting, or any adjournment thereof, and the number of votes which may be cast, will be determined by reference to WTW’s register of members as of 5:00 p.m. EDT on June 30, 2020, referred to as the “WTW Voting Record Time.” In each case, changes to WTW’s register of members after the WTW Voting Record Time shall be disregarded for the purposes of being entitled to vote.

If the form of proxy is duly completed and signed, and is submitted by following the instructions set forth on the proxy card no later than 11:59 p.m. EDT on August 25, 2020, or if a form of proxy is handed to the chairman of the WTW Court Meeting in Miami or to a representative of Matheson, legal advisors to WTW, in Dublin, before the start of the WTW Court Meeting, then it will be voted in the manner directed by the shareholder executing it, or if no directions are given, it will be voted “FOR” the proposals.

In the case of a corporation, limited liability company or partnership, the form of proxy must be either under its Common Seal or under the hand of an officer or attorney, duly authorized.

By the said Court Order, the Irish High Court has appointed John Haley or, failing him, Victor Ganzi, or, failing him, such director or officer of WTW or other person as the WTW board of directors, referred to as the “WTW Board,” may determine, to act as chairman of said WTW Court Meeting and has directed the chairman to report the result thereof to the Irish High Court.

Subject to the approval of the resolution proposed at the WTW Court Meeting convened by this Notice, the requisite resolutions to be proposed at the extraordinary general meeting of WTW convened for August 26, 2020 and the satisfaction of the other conditions to the completion of the scheme of arrangement, it is anticipated that the Irish High Court will order that the hearing of the application to sanction said scheme of arrangement will take place in the first half of 2021.

Terms shall have the same meaning in this Notice as they have in the joint proxy statement accompanying this Notice.

Said scheme of arrangement will be subject to the subsequent sanction of the Irish High Court.

Issued Shares and Total Voting Rights

The total number of issued Scheme Shares held by Scheme Shareholders as of the WTW Voting Record Time entitled to vote at the WTW Court Meeting is 128,762,994. The resolution at the WTW Court Meeting shall be decided on a poll. Every holder of a Scheme Share as of the WTW Voting Record Time will have one vote for every Scheme Share carrying voting rights of which he, she or it is the holder. A holder of a Scheme Share as of the WTW Voting Record Time (whether present in person or by proxy) who is entitled to more than one vote need not use all his, her or its votes or cast all his, her or its votes in the same way. In order for the resolution at the WTW Court Meeting to pass, those voting to approve the scheme must (a) represent a simple majority (being more than 50%) in number of the shareholders of record of Scheme Shares as of the WTW Voting Record Time present and voting (in person or by proxy), and (b) also represent 75% or more in value of the Scheme Shares held by such holders as of the WTW Voting Record Time, present and voting (in person or by proxy).

Irish law requires WTW to hold a physical meeting for the WTW Court Meeting. In light of COVID-19, WTW encourages WTW shareholders to vote by proxy prior to 11:59 p.m. EDT on August 25, 2020 as described

in the accompanying joint proxy statement. WTW asks that, in considering whether to attend the meeting in person, WTW shareholders follow public health and travel guidelines with respect to COVID-19, including as applicable to Ireland and the United States. Those guidelines may restrict or prevent any WTW shareholder from attending the meeting in person. WTW strongly encourages WTW shareholders not to attend the meeting in person if they are experiencing any of the described COVID-19 symptoms. WTW shareholders attending the WTW Court Meeting in person are also requested to follow the hygiene instructions consistent with applicable public health guidelines, including washing or disinfecting hands upon arrival at the meeting. WTW may take additional precautionary measures in relation to the WTW Court Meeting in response to further developments in the COVID-19 outbreak. WTW will be obliged to comply with any legal restrictions that are imposed as a consequence of COVID-19 and that affect the meeting, which may include preventing or restricting access to the meeting. WTW also intends to comply with any applicable public health and travel guidelines, which may affect the WTW Court Meeting. Depending on concerns about and developments relating to the COVID-19 outbreak, the WTW Board could determine to change the date, time, location or format of the WTW Court Meeting, subject to Irish legal requirements. In the event WTW determines it is necessary or appropriate to take additional steps regarding how the WTW Court Meeting will be conducted, WTW will announce such determinations in advance in accordance with applicable legal requirements, and details will be posted on WTW’s website and filed with the U.S. Securities and Exchange Commission.

YOUR VOTE IS IMPORTANT

IT IS IMPORTANT THAT AS MANY VOTES AS POSSIBLE ARE CAST AT THE WTW COURT MEETING (WHETHER IN PERSON OR BY PROXY) SO THAT THE IRISH HIGH COURT CAN BE SATISFIED THAT THERE IS A FAIR AND REASONABLE REPRESENTATION OF WTW SHAREHOLDER OPINION. TO ENSURE YOUR REPRESENTATION AT THE WTW COURT MEETING, YOU ARE REQUESTED TO COMPLETE, SIGN AND DATE THE ENCLOSED FORM OF PROXY AS PROMPTLY AS POSSIBLE AND RETURN IT IN THE POSTAGE PREPAID ENVELOPE ENCLOSED FOR THAT PURPOSE OR BY INTERNET OR TELEPHONE IN THE MANNER PROVIDED ABOVE. IF YOU ATTEND THE WTW COURT MEETING, YOU MAY VOTE IN PERSON EVEN IF YOU HAVE RETURNED A COMPLETED FORM OF PROXY.

Dated July 8, 2020

Matheson

70 Sir John Rogerson’s Quay

Dublin 2

Ireland

Solicitors for Willis Towers Watson plc

WILLIS TOWERS WATSON PLC

Willis Towers Watson House, Elm Park,

Merrion Road, Dublin 4, Ireland

NOTICE OF EXTRAORDINARY GENERAL MEETING OF WILLIS TOWERS WATSON PLC

NOTICE IS HEREBY GIVEN that an EXTRAORDINARY GENERAL MEETING, referred to as the “WTW EGM,” of Willis Towers Watson Public Limited Company, referred to as “WTW,” will be held at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States and Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland (where such participation in Ireland shall be by technological means, and shall constitute, in the case of attendance in either of such locations in the United States or Ireland, being present in person at the WTW EGM), on August 26, 2020, at 11:00 a.m., EDT (or, if the special Court-ordered meeting, referred to as the “WTW Court Meeting,” has not concluded by 11:00 a.m., EDT, as soon as possible after the conclusion or adjournment of the WTW Court Meeting) for the purpose of considering and, if thought fit, passing the following resolutions (of which resolutions 1, 3 and 4 will be proposed as ordinary resolutions and resolution 2 will be proposed as a special resolution):

That, subject to the approval by the requisite majorities at the WTW Court Meeting, the scheme of arrangement that is included in the document of which this Notice forms a part, referred to as the “scheme” or “scheme of arrangement,” (a copy of which has been produced to this meeting and for the purposes of identification signed by the chairman thereof), in its original form or with or subject to any modification, addition or condition approved or imposed by the High Court of Ireland be approved and the directors of WTW be authorized to take all such action as they consider necessary or appropriate for carrying the scheme of arrangement into effect.

That, subject to the scheme becoming effective, the articles of association of WTW, referred to as the “Articles,” be amended by adding the following new Article 171:

171. Scheme of Arrangement

on behalf of the new member and every form, instrument, or instruction executed or delivered or other such thing done so shall be as effective as if it has been executed, delivered or done by the new

member to which such form, instrument, instruction, or thing relates. Pending the registration of Aon and / or its nominee(s) as a holder of any share to be transferred under this Article 171, the new member shall not be entitled to exercise any rights attaching to any such share unless so agreed by Aon and Aon shall be irrevocably empowered to appoint a person nominated by Aon to act as attorney or agent on behalf of any holder of that share in accordance with any directions Aon may give in relation to any dealings with or disposal of that share (or any interest in it), the exercise of any rights attached to it or receipt of any distribution or other benefit accruing or payable in respect of it, and any holder(s) of that share must exercise all rights attaching to it in accordance with the directions of Aon. The Company shall not be obliged to issue a certificate to the new member for any such share.

That, on a non-binding, advisory basis, specified compensatory arrangements between WTW and its named executive officers relating to the transaction (as more particularly described in the section entitled “The Transaction—Interests of WTW Directors and Executive Officers in the Transaction” beginning on page 109 of the accompanying joint proxy statement) be approved.

That any motion by the chairman of the WTW EGM to adjourn the WTW EGM, or any adjournments thereof, to another time and place if necessary or appropriate to solicit additional proxies if there are insufficient votes at the time of the WTW EGM to approve resolutions 1 and 2, be approved.

By order of the board of directors of Willis Towers Watson plc

Willis Towers Watson plc, Willis Towers Watson House, Elm Park, Merrion Road, Dublin 4, Ireland

Dated: July 8, 2020

Notes:

Aon plc

Metropolitan Building

James Joyce Street, Dublin 1, Ireland D01 K0Y8

NOTICE OF EXTRAORDINARY GENERAL MEETING OF AON PLC

NOTICE IS HEREBY GIVEN that an EXTRAORDINARY GENERAL MEETING, referred to as the “Aon EGM” of Aon plc, referred to as “Aon,” will be held at 10:00 a.m., CDT (11:00 a.m., EDT), on August 26, 2020 at 200 East Randolph Street, Chicago, Illinois 60601, United States and, at the same time, Arthur Cox, Ten Earlsfort Terrace, Dublin 2, D02 T380, Ireland (where such participation in Ireland shall be by technological means), for the purpose of considering and, if thought fit, passing the following resolutions:

That the issuance of the aggregate scheme consideration pursuant to the transaction (as more particularly described in the accompanying joint proxy statement) be approved.

That any motion by the chair of the Aon EGM to adjourn the Aon EGM, or any adjournments thereof, to another time and place, if necessary or appropriate to solicit additional proxies if there are insufficient votes at the time of the Aon EGM to approve Resolution 1, be approved.

By order of the Board of Aon plc

Darren Zeidel

Company Secretary

July 8, 2020

Registered Office: Metropolitan Building, James Joyce Street, Dublin 1, Ireland D01 K0Y8

Notes:

As part of our precautions regarding the recent outbreak of COVID-19, we are sensitive to the public health and travel concerns that Aon shareholders may have, as well as any protocols that governmental entities may impose. Accordingly, we have made arrangements to enable persons to attend the Aon EGM virtually via the internet. The virtual attendance does not extend to voting at the Aon EGM. Irish law requires Aon to hold a physical meeting for the Aon EGM. In light of COVID-19, we strongly encourage Aon shareholders not to attend the Aon EGM in person, but to vote their Aon Shares in advance via the internet, by telephone, or by completing, signing and returning a form of proxy or voting instruction form, in each case as described in the accompanying joint proxy statement and, if you wish to hear the proceedings and ask questions, to do so virtually as described in the accompanying proxy statement. Aon asks that, in considering whether to attend the Aon EGM in person, Aon shareholders follow public health and travel guidelines with respect to COVID-19, including as applicable to Ireland and the United States. Those guidelines may restrict or prevent any Aon shareholder from attending the Aon EGM in person. Aon shareholders attending the Aon EGM in person are also requested to follow the hygiene instructions consistent with applicable public health guidelines, including washing or disinfecting hands upon arrival at the Aon EGM. Aon may take additional precautionary measures in relation to the Aon EGM in response to further developments in the COVID-19 outbreak. Aon will be obliged to comply with any legal restrictions that are imposed as a consequence of COVID-19 and that affect the Aon EGM, which may include preventing or restricting access to the Aon EGM. Aon also intends to comply with any applicable public health and travel guidelines, which may affect the Aon EGM. Depending on concerns about and developments relating to the COVID-19 outbreak, the Aon Board could determine to change the date, time, location or format of the Aon EGM, subject to Irish legal requirements. In the event Aon determines it is necessary or appropriate to take additional steps regarding how the Aon EGM will be conducted, we will announce such determinations in advance in accordance with applicable legal requirements, and details will be posted on our website and filed with the U.S. Securities and Exchange Commission.

REFERENCES TO ADDITIONAL INFORMATION

This joint proxy statement incorporates by reference important business and financial information about Aon plc, referred to as “Aon,” and Willis Towers Watson Public Limited Company, referred to as “WTW,” from documents that Aon and WTW have filed with the U.S. Securities and Exchange Commission, referred to as the “SEC,” and that are not included in or delivered with this joint proxy statement. For a listing of documents incorporated by reference herein and additional information on how you can obtain copies of these documents free of charge from Aon or WTW (as applicable), please see the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement. This information is also available for you to review free of charge through the SEC’s website at www.sec.gov.

This joint proxy statement is first being mailed to shareholders of Aon and WTW on or about July 8, 2020.

You also may request copies of this joint proxy statement and any of the documents incorporated by reference herein without charge by requesting them in writing from Aon or WTW (through its proxy solicitor) as follows:

In addition, if you have questions about the transaction or the special meetings, if you need assistance in submitting your proxy or voting your shares or if you need to obtain additional copies of this joint proxy statement, the enclosed proxy cards or other information related to the proxy solicitation, you should contact the applicable company’s proxy solicitor set forth below.

To receive timely delivery of the requested documents in advance of the extraordinary general meeting of Aon shareholders, referred to as the “Aon EGM,” the Court-convened meeting of WTW shareholders, referred to as the “WTW Court Meeting,” and/or the extraordinary general meeting of WTW shareholders, referred to as the “WTW EGM,” you should make your request no later than by 5:00 p.m., EDT, on August 19, 2020.

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QUESTIONS AND ANSWERS ABOUT THE TRANSACTION AND THE SPECIAL MEETINGS

The following questions and answers are intended to address briefly some commonly asked questions regarding the transaction and the special meetings. These questions and answers highlight only some of the information contained in this joint proxy statement. They may not contain all the information that is important to you. You should read carefully this entire joint proxy statement, including the annexes and the documents incorporated by reference herein, to understand fully the transaction and the voting procedures for the special meetings. See the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement. Unless otherwise specified, each reference in this joint proxy statement to: “Aon Ireland” refers to Aon plc (formerly known as Aon Limited), a public limited company incorporated in Ireland with registered number 604607; “Aon UK” refers to Aon plc, a public limited company incorporated in England with registered number 07876075; “Aon” refers to Aon UK (prior to the assignment on April 2, 2020 of the Business Combination Agreement from Aon UK to Aon Ireland) and Aon Ireland (after such assignment); the “Aon Board” refers to the board of directors of Aon UK prior to the effective date of the Aon reorganization and to the board of directors of Aon Ireland after the effective date of the Aon reorganization; “WTW” refers to Willis Towers Watson Public Limited Company, a public limited company incorporated in Ireland with registered number 475616; the “Business Combination Agreement” refers to the Business Combination Agreement, dated as of March 9, 2020, by and between WTW and Aon (all of Aon’s rights and obligations thereunder have been assigned to Aon Ireland in accordance therewith), a copy of which is attached as Annex A to this joint proxy statement; the “conditions appendix” refers to the conditions to the transaction and the scheme, a copy of which is attached as Annex B to this joint proxy statement; the “Expenses Reimbursement Agreement” refers to the Expenses Reimbursement Agreement, dated as of March 9, 2020, by and between WTW and Aon (all of Aon UK’s rights and obligations thereunder have been assigned to Aon Ireland in accordance therewith), a copy of which is attached as Annex C to this joint proxy statement. Unless otherwise indicated, all references to “dollars” or “$” in this joint proxy statement are references to U.S. dollars.

If you are in any doubt about the transaction, you should consult an independent financial advisor who, if you are taking advice in Ireland, is authorized or exempted by the Investment Intermediaries Act 1995 (as amended), or the European Union (Markets in Financial Instruments) Regulations 2017 (S.I. No. 375 of 2017).

The holder of each issued and outstanding ordinary share, nominal value $0.000304635 per share, of WTW, referred to collectively as the “WTW Shares,” that is subject to the scheme will be entitled to receive 1.08 Class A ordinary shares, nominal value $0.01 per share, of Aon, referred to collectively as the “Aon Shares,” in exchange for such WTW Share, such ratio referred to as the “exchange ratio,” pursuant to the scheme and as more particularly described under the section entitled “The Business Combination Agreement—Scheme Consideration to WTW Shareholders” beginning on page 131 of this joint proxy statement. The implied value of the scheme consideration to WTW shareholders, calculated by multiplying the closing price of an Aon Share on the relevant date by the exchange ratio of 1.08 Aon Shares for each WTW Share, was $184.28 per WTW Share, as of March 4, 2019, the day before the initial market rumors and Aon’s announcement of the parties’ initial exploration of a potential transaction, $231.99 per WTW Share, as of March 6, 2020, the last trading day prior to the announcement of the transaction and $208.01 per WTW Share, as of June 30, 2020, the last practicable trading day before the date of this joint proxy statement.

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The High Court of Ireland, referred to as the “Irish High Court,” has ordered the convening of a special Court-ordered meeting of WTW shareholders, referred to as the “WTW Court Meeting,” at 10:30 a.m., EDT on August 26, 2020 in order to obtain shareholder approval of the scheme. In addition, WTW will hold an extraordinary general meeting of shareholders, referred to as the “WTW EGM,” at 11:00 a.m., EDT on August 26, 2020 or, if the WTW Court Meeting has not concluded by 11:00 a.m., EDT as soon as possible after the conclusion or adjournment of the WTW Court Meeting, in order to obtain shareholder approval of the resolutions necessary to implement the scheme and related resolutions.

It will not be possible to complete the transaction unless the requisite WTW shareholder approvals and Aon shareholder approvals described under the sections entitled “The Special Meetings of WTW Shareholders—Proposals” and “The Extraordinary General Meeting of Aon Shareholders—Proposals” beginning on pages 56 and 63 of this joint proxy statement, respectively, are obtained at each special meeting.

Your vote is required in connection with the transaction and, as a result, Aon and WTW are each holding special meetings of their shareholders in order to obtain the required shareholder approvals. A copy of the Business Combination Agreement is attached as Annex A to this joint proxy statement. To review the full terms of the scheme, see the section entitled “Part 3—The Scheme of Arrangement” beginning on page 212 of this joint proxy statement.

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Aon shareholders. You may also hear the proceedings of the Aon EGM, and submit your questions prior to and during the Aon EGM, virtually by visiting www.meetingcenter.io/233091301 at the time of the Aon EGM and entering the 15-digit control number on your proxy card and the meeting password: AON2020. We encourage you to access the Aon EGM virtually prior to the start time and leave ample time for the check-in. If you attend the meeting as a “guest,” you will not be able to submit questions prior to or during the Aon EGM. Note that virtual attendance will not allow you to vote at the Aon EGM, so we strongly encourage Aon shareholders to vote their Aon Shares in advance via one of the methods described above.

If you are a registered shareholder, you do not need to register to attend the Aon EGM virtually; simply follow the instructions on your proxy card. If you hold your Aon Shares through an intermediary, such as a bank or broker, you must register in advance to attend the Aon EGM virtually. To do so, you must submit proof of your proxy power, or legal proxy, reflecting your holdings of Aon Shares along with your name and email address to Computershare Trust Company N.A. Requests for registration must be labeled as “Legal Proxy” and be received no later than August 21, 2020. To request registration, please forward the email from your bank or broker, or attach an image of your legal proxy, to legalproxy@computershare.com. You will receive a confirmation of your registration by email from Computershare Trust Company N.A. after your registration has been received. Beneficial owners without a legal proxy can attend the meeting as a “guest” but will not be able to ask questions.

WTW. The WTW Court Meeting will be held on August 26, 2020, at 10:30 a.m., EDT. The WTW Court Meeting will be held at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States and Scheme Shareholders (as defined in the section entitled “Part 3—The Scheme of Arrangement” beginning on page 212 of this joint proxy statement) (or their proxies) may also participate in the WTW Court Meeting in Ireland at Matheson, 70 Sir John Rogerson’s Quay, Dublin 2 (where such participation in Ireland shall be by technological means, and shall constitute, in the case of attendance in either of such locations, being present in person at the WTW Court Meeting).

The WTW EGM will be held on August 26, 2020, at 11:00 a.m., EDT or, if the WTW Court Meeting has not concluded by 11:00 a.m., EDT, as soon as possible after the conclusion or adjournment of the above mentioned WTW Court Meeting. The WTW EGM will be held at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States and WTW shareholders may also participate in the WTW EGM in Ireland at Matheson, 70 Sir John Rogerson’s Quay, Dublin 2 (where such participation in Ireland shall be by technological means, and shall constitute, in the case of attendance in either of such locations, being present in person at the WTW EGM).

At the WTW Court Meeting, WTW shareholders (excluding Aon and its affiliates, to the extent they hold WTW Shares) will be asked to approve the scheme for the purposes of satisfying the requirements of the Irish legislation upon which the scheme is based.

At the WTW EGM, WTW shareholders (including Aon and its affiliates, to the extent they hold WTW Shares) will also be asked to approve the scheme, authorize WTW’s directors to take whatever actions they

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deem necessary or appropriate for carrying the scheme into effect and approve other related matters. For more detail on these matters, see the section entitled “The Special Meetings of WTW Shareholders” beginning on page 55 of this joint proxy statement.

Each of the resolutions to be considered at the Aon EGM is an “ordinary resolution,” the approval of which requires the approval of at least a majority of the votes cast by the holders of Aon Shares present and voting, either in person or by proxy.

Because the votes required to approve each of the resolutions are based on votes properly cast at the Aon EGM, and because abstentions are not considered votes properly cast, abstentions, along with failures to vote, will have no effect on the approval of the resolutions.

As of 5:00 p.m. EDT on June 30, 2020, Aon directors and executive officers had the right to vote approximately 2,298,921 Aon Shares at the Aon EGM, representing approximately 0.99% of the Aon Shares entitled to vote at the Aon EGM. It is expected that all Aon directors and executive officers will vote “FOR” each of the proposals at the Aon EGM.

WTW. WTW Court Meeting. WTW shareholders are being asked to vote on a proposal to approve the scheme at both the WTW Court Meeting and the WTW EGM, referred to as the “Court Meeting resolution.” However, the vote required for such proposal is different at each of the meetings. As set out in full under the section entitled “Part 2—Explanatory Statement—Consents and Special Meetings” beginning on page 196 of this joint proxy statement, in order for the resolution at the WTW Court Meeting to pass, those voting to approve the scheme must: (a) represent a simple majority (being more than 50%) in number of the WTW shareholders of record as of 5:00 p.m., EDT, on June 30, 2020, referred to as the “WTW Voting Record Time,” present and voting (in person or by proxy), and (b) also represent 75% or more in value of the WTW Shares held by such holders as of the WTW Voting Record Time, present and voting (in person or by proxy).

Because the vote required to approve the proposal at the WTW Court Meeting is based on votes properly cast at the WTW Court Meeting, and because abstentions are not considered votes properly cast, abstentions, along with failures to vote, will have no effect on the approval of such proposal. The transaction is conditioned on approval of the scheme at the WTW Court Meeting.

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WTW EGM. Set forth below is a table summarizing certain information with respect to the resolutions to be voted on at the WTW EGM, referred to as the “WTW EGM resolutions” (the first two of which are referred to as the “required WTW EGM resolutions”):

At the WTW EGM, the requisite approval of each of the resolutions depends on whether it is (i) an “ordinary resolution” (the Scheme Approval Resolution, the Compensation Resolution and the Adjournment Resolution), which requires the approval of at least a majority of the votes cast by the holders of WTW Shares present and voting, either in person or by proxy, or (ii) a “special resolution” (the Constitution Amendment Resolution), which requires the approval of at least 75% of the votes cast by the holders of WTW Shares present and voting, either in person or by proxy.

Because the votes required to approve each of the resolutions are based on votes properly cast at the WTW EGM, and because abstentions are not considered votes properly cast, abstentions, along with failures to vote, will have no effect on the approval of the resolutions.

As of 5:00 p.m. EDT on June 30, 2020, WTW directors and executive officers had the right to vote approximately 466,576 WTW Shares at the WTW special meetings, representing approximately 0.36% of the WTW Shares entitled to vote at each of such meetings. It is expected that all WTW directors and executive officers will vote “FOR” each of the proposals at the WTW Court Meeting and “FOR” each of the proposals at the WTW EGM.

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WTW. Yes. It is important that as many votes as possible are cast at the WTW Court Meeting and the WTW EGM (whether in person or by proxy) so that the Irish High Court can be satisfied that there is a fair and reasonable representation of WTW shareholder opinion and to ensure that the views of WTW shareholders are heard. To ensure your representation at the WTW Court Meeting and the WTW EGM, you are requested to complete, sign and date the enclosed form of proxy as promptly as possible and return it in the postage prepaid envelope enclosed for that purpose or vote by internet or telephone in the manner provided above. If you attend the WTW Court Meeting or the WTW EGM in person, you may vote at such meeting even if you have previously returned a completed form of proxy.

Quorum for Aon special meeting. A quorum will exist with respect to each matter to be considered at the Aon EGM if the holders of Aon Shares representing a majority of the Aon Shares issued and outstanding as of 5:00 p.m. EDT on June 30, 2020, referred to as the “Aon Voting Record Time,” are present in person or by proxy and entitled to vote. Aon Shares held in “street name” will be counted as present for the purpose of determining the existence of a quorum at the Aon EGM so long as an Aon shareholder has given its bank, broker or other nominee voting instructions on at least one proposal to come before the Aon EGM. Abstentions, though counted for the purposes of determining that a quorum is present, will not be counted as votes cast and therefore will have no effect on the approval of the resolutions.

Quorum for WTW special meetings. A quorum will exist with respect to each matter to be considered at the WTW Court Meeting and the WTW EGM if the holders of WTW Shares representing at least 50% of the WTW Shares issued and outstanding at the WTW Voting Record Time, each being a holder of WTW Shares as of the WTW Voting Record Time, a proxy for a holder of WTW Shares as of the WTW Voting Record Time or a duly authorized representative of a corporate holder of WTW Shares as of the WTW Voting Record Time, are present in person or by proxy and entitled to vote, provided however that if a class of shareholders has only one shareholder, then one shareholder present in person or by proxy shall constitute the necessary quorum. WTW Shares held in “street name” will be counted as present for the purpose of determining the existence of a quorum at the WTW Court Meeting and the WTW EGM so long as a shareholder has given its bank, broker or other nominee voting instructions on at least one of the proposals, or resolutions, as applicable, brought before the applicable meeting. Abstentions, though counted for the purposes of determining that a quorum is present, will not be counted as votes cast and therefore will have no effect on the approval of the proposals or resolutions, as applicable.

The Aon Board unanimously recommends that Aon shareholders vote:

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See the section entitled “The Transaction—Recommendation of the Aon Board and Aon’s Reasons for the Transaction” beginning on page 79 of this joint proxy statement.

WTW. The WTW Board has unanimously approved the Business Combination Agreement and determined that the Business Combination Agreement and the transaction contemplated by the Business Combination Agreement, including the scheme, are advisable and in the best interests of WTW and its shareholders and that the terms of the scheme are fair and reasonable.

The WTW Board unanimously recommends that WTW shareholders vote:

See the section entitled “The Transaction—Recommendation of the WTW Board and WTW’s Reasons for the Transaction” beginning on page 83 of this joint proxy statement.

In considering the recommendation of the WTW Board, you should be aware that certain WTW directors and executive officers have interests in the transaction that are in addition to, or different from, the interests they might have as WTW shareholders generally. See the section entitled “The Transaction—Interests of WTW Directors and Executive Officers in the Transaction” beginning on page 109 of this joint proxy statement.

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WTW. All holders of record of WTW Shares as of the WTW Voting Record Time, which is 5:00 p.m. EDT on June 30, 2020 will be entitled to receive notice of, and to vote at, the WTW Court Meeting and the WTW EGM and any adjournments thereof. Attending the WTW Court Meeting and the WTW EGM in person is not required to vote. See the sections entitled “Questions and Answers About The Transaction and the Special Meeting—How can I vote my shares without attending the special meetings?” and “Questions and Answers About The Transaction and the Special Meeting—Are any special measures being taken at the special meetings as a result of the current COVID-19 outbreak?” beginning on pages 3 and 11 of this joint proxy statement, respectively, for instructions on how to vote your WTW Shares without attending the WTW Court Meeting or WTW EGM in person.

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For U.S. federal income tax purposes, the transaction is intended to qualify as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, referred to as the “Code.” Provided that the transaction so qualifies, a holder of WTW Shares generally will not recognize any gain or loss for U.S. federal income tax purposes on the exchange of such WTW Shares for Aon Shares in the transaction, except with respect to any cash received in lieu of fractional Aon Shares. A holder of WTW Shares generally will recognize gain or loss for U.S. federal income tax purposes with respect to cash received in lieu of a fractional Aon Share in the transaction measured by the difference, if any, between the amount of cash received for such fractional Aon Share and the holder’s tax basis in such fractional Aon Share.

For a more detailed discussion of the material U.S. federal income tax consequences, please carefully review the information set forth in the section entitled “Material Tax Consequences of the Transaction—Material U.S. Federal Income Tax Considerations” beginning on page 122 of this joint proxy statement.

The tax consequences of the transaction to any particular WTW shareholder will depend on such shareholder’s particular facts and circumstances. Accordingly, we strongly urge you to consult your tax advisor for a full understanding of the particular tax consequences of the transaction to you.

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Aon and WTW have agreed to coordinate with each other on the payment of dividends in respect of Aon Shares and WTW Shares such that holders of WTW Shares do not receive dividends on both the Aon Shares received in the transaction, as well as their WTW Shares, in respect of the same calendar quarter or fail to receive a dividend on either Aon Shares received in the transaction or their WTW Shares in respect of any calendar quarter. The agreement reached between Aon and WTW in relation to dividends in the Business Combination Agreement does not apply to any quarterly dividend of either Aon or WTW not reasonably expected to be paid on or around the closing. See the section entitled “The Business Combination Agreement—Covenants and Agreements—Dividends and Distributions” beginning on page 144 of this joint proxy statement.

If you are a beneficial owner of Aon Shares but not the shareholder of record of such shares (for example, if such shares are held in “street name” by a bank, broker or other nominee), you will also need proof of your ownership of such shares as of the Aon Voting Record Time to be admitted to the Aon EGM. A recent brokerage statement or a letter from a bank or broker are examples of proof of ownership. You will not be permitted to vote at the Aon EGM in person unless you first obtain a legal proxy issued in your name from the record owner and present it to the inspector of election with your ballot at the Aon EGM. To request a legal proxy, contact your bank, broker or other nominee holder of record. It is suggested you do so in a timely manner to ensure receipt of your legal proxy prior to the Aon EGM.

Failure to bring the appropriate documentation may delay your entry into or prevent you from attending or voting in person at the Aon EGM. See the sections entitled “The Extraordinary General Meeting of Aon Shareholders—Attendance” and “Questions and Answers About The Transaction and the Special Meeting—Are any special measures being taken at the special meetings as a result of the current COVID-19 outbreak?” beginning on pages 62 and 12 of this joint proxy statement, respectively.

WTW. WTW Shares held directly in your name as the shareholder of record as of the WTW Voting Record Time may be voted in person at the WTW Court Meeting and the WTW EGM. Those entitled to attend and vote at the WTW Court Meeting and the WTW EGM may attend at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131, United States, or Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland (where such participation in Ireland shall be by technological

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means, and shall constitute, in the case of attendance in either of such locations, being present in person at the WTW Court Meeting or the WTW EGM, as the case may be). If you choose to attend either or both WTW special meetings in person, you will need to bring proof of identification and address.

If you are a beneficial owner of WTW Shares but not the shareholder of record of such shares (for example, if your shares are held in “street name” by a bank, broker or other nominee), you will also need proof of your ownership of such shares as of the WTW Voting Record Time to be admitted to the WTW special meetings. A recent brokerage statement or a letter from a bank or broker are examples of proof of ownership. You will not be permitted to vote at the WTW Court Meeting or the WTW EGM in person unless you first obtain a legal proxy issued in your name from the record owner and present it to the inspector of election in Miami or to a representative of Matheson, legal advisors to WTW, in Dublin, with your ballot at the applicable WTW special meeting. To request a legal proxy please contact your bank, broker or other nominee holder of record. It is suggested you do so in a timely manner to ensure receipt of your legal proxy prior to the applicable WTW special meeting.

Failure to bring the appropriate documentation may delay your entry into or prevent you from attending or voting in person at the WTW Court Meeting or the WTW EGM. See the sections entitled “The Special Meetings of WTW Shareholders—Attendance and Voting” and “Questions and Answers About The Transaction and the Special Meetings—Are any special measures being taken at the special meetings as a result of the current COVID-19 outbreak?” beginning on pages 55 and 12 of this joint proxy statement, respectively.

If your Aon Shares are held in an account through a bank, broker or other nominee, you must instruct the bank, broker or other nominee how to vote such shares by following the instructions that the bank, broker or other nominee provides you along with this joint proxy statement. Your bank, broker or other nominee, as applicable, may have an earlier deadline by which you must provide instructions to it as to how to vote such shares, so you should carefully read the materials provided to you by your bank, broker or other nominee.

In the case of joint holders, the vote of the senior member who tenders a vote, whether in person or by proxy, will be accepted to the exclusion of the votes of the other joint holders of record and, for this purpose, seniority will be determined by the order in which the names appear in Aon’s register of members in respect of the joint holding.

In light of COVID-19, Aon strongly encourages Aon shareholders not to attend the Aon EGM in person, but to vote their Aon Shares in advance via the internet, by telephone, or by completing, signing and returning a form of proxy or voting instructions form and, if you wish to hear the proceedings and ask questions, to do so virtually. See the sections entitled “Questions and Answers About The Transaction and the Special Meetings—When and where will each special meeting be held?” and “Questions and Answers About The Transaction and the Special Meetings—Are any special measures being taken at the special meetings as a result of the current COVID-19 outbreak?” beginning on pages 3 and 12 of this joint proxy statement, respectively, for a discussion of how attendance in person at the Aon EGM may be affected by the current COVID-19 outbreak.

WTW. If you are a WTW shareholder of record as of the WTW Voting Record Time, you will receive two proxy cards (one for the WTW Court Meeting and one for the WTW EGM). You may vote your WTW Shares in one of the following ways:

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If your WTW Shares are held in “street name,” you should follow the instructions provided by your bank, broker or other nominee in order to instruct them how to vote such shares. The bank, broker or other nominee, as applicable, may have an earlier deadline by which you must provide instructions to it as to how to vote such shares, so you should carefully read the materials provided to you by your bank, broker or other nominee.

In the case of joint holders, the vote of the senior member who tenders a vote, whether in person or by proxy, will be accepted to the exclusion of the votes of the other joint holders of record and, for this purpose, seniority will be determined by the order in which the names appear in WTW’s register of members in respect of the joint holding.

In light of COVID-19, WTW encourages WTW shareholders to vote their WTW Shares via the internet, by telephone, or by completing, signing and returning a form of proxy or voting instructions form. See the section entitled “Questions and Answers About The Transaction and the Special Meeting—Are any special measures being taken at the special meetings as a result of the current COVID-19 outbreak?” beginning on page 12 of this joint proxy statement for a discussion of how attendance in person at the WTW Court Meeting and the WTW EGM may be affected by the current COVID-19 outbreak.

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WTW. If your WTW Shares are registered directly in your name with WTW’s transfer agent, Computershare Trust Company N.A., you are considered the shareholder of record with respect to such shares, and access to proxy materials is being provided directly to you. If your WTW Shares are held by a bank, in a stock brokerage account or by another nominee, then you are considered the beneficial owner of such shares, which are considered to be held in “street name.” Access to proxy materials is being provided to you by your bank, broker or other nominee, who is considered the shareholder of record with respect to such shares.

A “broker non-vote” occurs when a broker submits a proxy that states that the broker does not vote for one or more of the proposals because (i) the broker has not received instructions from the beneficial owner on how to vote the applicable shares with respect to those proposals and (ii) the broker does not have discretionary authority to vote the shares in the absence of instructions. Because brokers will not have discretionary authority to vote on any of the proposals at the special meetings, no “broker non-votes” can occur at any of the special meetings.

Please see the sections entitled “The Special Meetings of WTW’s Shareholders—Voting WTW Shares Held in Street Name” and “The Extraordinary General Meeting of Aon Shareholders—Voting Aon Shares Held in Street Name” beginning on pages 60 and 65 of this joint proxy statement, respectively.

WTW. Each WTW shareholder of record is entitled to one vote for each WTW Share held of record by him or her as of the WTW Voting Record Time.

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WTW. If you sign and return your proxy card appointing the named proxies of the applicable special meeting as your proxy but do not mark the proxy card to tell the proxy how to vote on a particular proposal, then your WTW Shares will be voted “FOR” such proposal.

If you sign and return your proxy card(s) appointing the named proxies of the applicable special meeting as your proxy but do not mark the proxy card(s) to tell the proxy how to vote on a particular proposal, such shares will be voted “FOR” such proposal.

If you hold your shares through a bank, broker or other nominee, you should follow the instructions provided by your bank, broker or other nominee when instructing them how to vote your shares.

If you are a shareholder of record, please sign the relevant proxy card(s) exactly as your name appears on the card. In the case of joint holders, the vote of the senior member who tenders a vote, whether in person or by proxy, will be accepted to the exclusion of the vote(s) of the other joint holder(s) and, for this purpose, seniority will be determined by the order in which the names stand in the register of members of WTW or Aon, as applicable, in respect of the joint holding. If you are a shareholder that is a corporation, limited liability company or partnership, the form of proxy must be either under its Common Seal or under the hand of an officer or attorney, duly authorized. If the relevant proxy card(s) are signed pursuant to a power of attorney or by an executor, administrator, trustee or guardian, please state the signatory’s full title and provide a certificate or other proof of appointment.

If your shares are held through a WTW employee share plan, you must vote such shares prior to 11:59 p.m. EDT on August 23, 2020. You should contact the trustee of your plan for additional information on voting your shares held through a WTW employee share plan.

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If your shares are held though an Aon employee share plan, you should contact the trustee of your plan if you have questions about voting your shares held through an Aon employee share plan.

If your Aon Shares are held in “street name” by a bank, broker or other nominee, you should follow the instructions of your bank, broker or other nominee regarding the revocation of proxies.

Attendance at the Aon EGM will not, in and of itself, revoke a proxy or change your voting instructions; you must vote by ballot at the Aon EGM to change your vote.

WTW. Yes, WTW shareholders may change their vote at any time before their proxy is voted at the WTW Court Meeting or at any time before their proxy is voted at the WTW EGM. If you are a registered shareholder (i.e., a shareholder who holds shares directly with WTW’s transfer agent in his, hers or its own name), you may revoke your proxy before the meeting by:

If you are a beneficial shareholder (i.e., your shares are held in the name of a bank, broker or other holder of record, sometimes referred to as holding shares in “street name”), follow the voting instructions provided to you by such bank, broker or other holder of record to determine how you may change your vote or revoke your proxy.

Simply attending the applicable meeting, however, will not revoke your proxy or change your voting instructions; you must vote by ballot at the applicable meeting to change your vote.

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WTW. The WTW Board is soliciting proxies from WTW shareholders in connection with the WTW Court Meeting and the WTW EGM. WTW has retained Innisfree M&A Incorporated, referred to as “Innisfree,” to assist in the solicitation process. WTW will pay Innisfree a fee of up to $75,000, as well as reasonable and documented out-of-pocket expenses. Under the Business Combination Agreement, Aon and WTW will each bear 50% of the costs incurred in connection with the solicitation of proxies in connection with the WTW Court Meeting and the WTW EGM.

If your shares are held by a broker, bank or other nominee, you should contact your broker, bank or other nominee for additional information.

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RISK FACTORS

You should carefully consider all of the information contained or incorporated by reference in this joint proxy statement, including the matters addressed under the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 47 of this joint proxy statement. In addition, Aon shareholders should carefully consider the following risks before deciding how to vote with respect to the proposals to be considered and voted on at the Aon EGM, and WTW shareholders should carefully consider the following risks before deciding how to vote with respect to the proposals to be considered and voted on at the WTW Court Meeting and the WTW EGM. Aon shareholders and WTW shareholders should also read and consider the risks associated with the businesses of each of Aon and WTW because these risks will also affect the combined company. The risks associated with the business of Aon can be found in Aon’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019 and Quarterly Report on Form 10-Q for the fiscal quarter ended March 31, 2020, each of which is incorporated by reference in this joint proxy statement. The risks associated with the business of WTW can be found in WTW’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019 and Quarterly Report on Form 10-Q for the fiscal quarter ended March 31, 2020, each of which is incorporated by reference in this joint proxy statement. See the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement.

Risks Relating to the Transaction

Because the market price of Aon Shares will fluctuate, WTW shareholders cannot be sure of the market price of the Aon Shares they will receive.

At the effective time, WTW shareholders will be entitled to receive 1.08 Aon Shares in exchange for each WTW Share held by such WTW shareholders (as well as cash in lieu of any fractional shares). The number of Aon Shares that WTW shareholders will be entitled to receive will not be adjusted in the event of any increase or decrease in the share price of either the Aon Shares or the WTW Shares at any time prior to the closing of the transaction, including between the time WTW shareholders vote to approve the scheme and the closing.

The market value of the Aon Shares that WTW shareholders will be entitled to receive at the closing of the transaction could vary significantly from the market value of the Aon Shares on the date of this joint proxy statement or the date on which WTW shareholders vote to approve the scheme. Because the exchange ratio will not be adjusted to reflect any changes in the market value of the Aon Shares or the WTW Shares, such market price fluctuations may affect the value that WTW shareholders will be entitled to receive upon the closing of the transaction. Share price changes may result from a variety of factors, including changes in the business, operations or prospects of Aon or WTW, market assessments of the likelihood that the transaction will be completed, the timing of the transaction, regulatory considerations, general market and economic conditions and other factors, including the effect of COVID-19 on the global economy or stock market. Such factors are difficult to predict and in many cases may be beyond the control of Aon or WTW. Consequently, at the time WTW shareholders must decide whether to approve the transaction and related proposals, they will not know the actual market value of the consideration they will receive for each of their WTW Shares at the closing.

The actual value of the consideration received by WTW shareholders at the closing will depend on the market value of the Aon Shares at that time. This market value may differ, possibly materially, from the market value of Aon Shares at the time the Business Combination Agreement was entered into or at any other time. WTW shareholders should obtain and consider current stock quotations for Aon Shares, which are traded on the NYSE under the ticker symbol, “AON,” and WTW Shares, which are traded on NASDAQ under the ticker symbol “WLTW,” before voting their WTW Shares. For additional information about the scheme consideration, see the section entitled “The Transaction—Scheme Consideration to WTW Shareholders” beginning on page 67 of this joint proxy statement.

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The market price of Aon Shares will continue to fluctuate after the transaction closes.

Upon the closing of the transaction, holders of WTW Shares will become holders of Aon Shares. The market price of Aon Shares may fluctuate significantly following the closing of the transaction and holders of WTW Shares could lose some or all of the value of the Aon Shares they will receive. In addition, any significant price or volume fluctuations in the stock market generally could have a material adverse effect on the market for, or liquidity of, the Aon Shares, regardless of Aon’s actual operating performance.

The market price of Aon Shares may be affected by factors different from those that historically have affected shares of WTW Shares.

Upon the closing of the transaction, holders of WTW Shares will become holders of Aon Shares. The business of Aon differs from, and is complementary to, that of WTW, and, accordingly, the financial position or results of operations or cash flows of Aon following the transaction, as well as the market price of Aon Shares, may be affected by factors different from those currently affecting the financial position or results of operations or cash flows of WTW. Following the closing of the transaction, WTW will be part of a larger company with other lines of business and a broader geographic footprint, so decisions that affect WTW may be made in respect of the larger combined business as a whole rather than the WTW business individually.

The transaction is subject to customary closing conditions, including conditions related to required shareholder approvals and required regulatory approvals, and may not be completed on a timely basis, or at all, or may be completed on a basis that has a material impact on the value of the combined company.

The closing of the transaction is subject to a number of customary conditions, and there can be no assurance that the conditions to the closing of the transaction will be satisfied or waived (to the extent applicable). The failure to satisfy the required conditions could delay the closing of the transaction for a significant period of time or prevent the closing of the transaction from occurring at all. These closing conditions include, among others, the receipt of required approvals of Aon shareholders and WTW shareholders and the approval of the scheme by the Irish High Court. These closing conditions also include certain antitrust related clearances, including under the HSR Act, the EC Merger Regulation and the antitrust laws of the other required antitrust jurisdictions. These closing conditions also include certain other regulatory clearances, which are described in more detail in the section entitled “The Transaction—Regulatory Approvals Required—Other Required Regulatory Clearances” beginning on page 117 of this joint proxy statement.

The governmental agencies from which the parties will seek certain approvals related to these conditions have broad discretion in administering the applicable governing regulations. As a condition to their approval of the transaction, agencies may impose requirements, limitations or costs or require divestitures or place restrictions on the conduct of the combined company’s business after the closing of the transaction. Such requirements, limitations, costs or restrictions could delay or prevent the closing of the transaction or have a material adverse effect on the combined company’s business and results of operations following the closing of the transaction.

In addition, the closing conditions include other legal and regulatory conditions, such as (i) the sanction by the Irish High Court of the scheme and the delivery of the court order to the Irish Registrar of Companies, (ii) the approval by the NYSE of the listing of all of the Aon Shares to be issued in connection with the scheme and (iii) the absence of any law or order that restrains, enjoins, makes illegal or otherwise prohibits the closing of the transaction.

The transaction is also subject to other customary closing conditions, including: (i) the Business Combination Agreement not having been terminated in accordance with its terms; (ii) the accuracy of each party’s representations and warranties made in the Business Combination Agreement, subject to specified materiality standards; (iii) the absence of a material adverse effect with respect to each party since March 9,

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2020; and (iv) the performance and compliance by each party of all of its obligations and compliance with all of its covenants under the Business Combination Agreement in all material respects. For a more complete summary of the conditions that must be satisfied or waived prior to the closing of the transaction, see the section entitled “The Business Combination Agreement—Conditions to the Closing of the Transaction” beginning on page 144 of this joint proxy statement. There can be no assurance that the conditions to the closing of the transaction will be satisfied or waived or that the transaction will be completed within the expected time frame, or at all.

In addition, if the transaction is not completed by March 9, 2021 (or June 9, 2021 or September 9, 2021, if extended under the terms of the Business Combination Agreement, if applicable, or such earlier date as may be specified by the Irish Takeover Panel), either Aon or WTW may choose not to proceed with the transaction. The parties can mutually decide to terminate the Business Combination Agreement at any time, before or after the receipt of Aon or WTW shareholder approval. See the section entitled “The Business Combination Agreement—Termination” beginning on page 146 of this joint proxy statement for more detail on these and other circumstances in which Aon and WTW may elect to terminate the Business Combination Agreement.

The Business Combination Agreement contains provisions that limit WTW’s and Aon’s ability to pursue alternatives to the transaction and, in specified circumstances, could require WTW to reimburse certain of Aon’s expenses or Aon to reimburse certain of WTW’s expenses.

Under the Business Combination Agreement, Aon and WTW are each subject to certain restrictions on its ability to solicit alternative acquisition proposals from third parties, engage in discussion or negotiations with respect to such proposals or provide information in connection with such proposals, subject to customary exceptions. Neither Aon nor WTW may terminate the Business Combination Agreement in order to enter into an agreement providing for a superior proposal. While either the Aon Board or the WTW Board, as applicable, may change its recommendation in respect of supporting the transaction as a result of unsolicited proposals received from third parties, subject to compliance with the terms of the Business Combination Agreement, no such change in recommendation will relieve Aon or WTW, as applicable, from its obligation to submit to its shareholders the proposals set forth in this joint proxy statement at the applicable special meetings. In addition, if such a change in recommendation is made at certain times, then the other party has a right to terminate the Business Combination Agreement and, under certain circumstances, the party whose board of directors effected the change in recommendation may have an obligation to reimburse certain of the other party’s transaction expenses in accordance with the terms of the Expenses Reimbursement Agreement. See the sections entitled “The Business Combination Agreement—Covenants and Agreements—No Solicitation by Aon or WTW” and “The Expenses Reimbursement Agreement” beginning on pages 136 and 149 of this joint proxy statement, respectively. These provisions could discourage a third party that may have an interest in acquiring all or a significant part of Aon or WTW from considering or proposing that acquisition, even if such third party were prepared to pay consideration with a higher value than the value of the scheme consideration.

Failure to close the transaction could negatively impact the share price and the future business and financial results of Aon and/or WTW.

If the transaction is not completed for any reason, including the failure of Aon shareholders or WTW shareholders to approve the required proposals at their respective special meetings, the ongoing business of Aon and/or WTW may be adversely affected and, without realizing any of the potential benefits of having closed the transaction, Aon and/or WTW will be subject to a number of risks, including the following:

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If the transaction does not close, these risks may materialize and may adversely affect Aon’s and/or WTW’s business, financial results and share price.

Certain Aon and WTW directors and executive officers may have interests in the transaction that are in addition to, or different from, the interests they might have as Aon shareholders or WTW shareholders, respectively.

In considering the recommendation of the Aon and WTW boards of directors with respect to the Business Combination Agreement, you should be aware that certain Aon and WTW directors and executive officers may have interests in the transaction that are in addition to, or different from, the interests they might have as Aon shareholders generally or WTW shareholders generally, respectively. These interests include, for WTW directors and officers, among others, the vesting of equity awards held by WTW non-employee directors at the effective time and for executive officers, the vesting of equity awards and payment of severance benefits upon certain qualifying terminations of employment during a specified period following a change in control of WTW, and any compensation received, following the closing of the transaction, by any WTW directors or executive officers that continue their board membership or their employment with Aon following the closing. As of the date of this joint proxy statement, there has been no agreement between Aon and any such individuals regarding any such compensation or the terms of any such service or employment (except, in the case of Mr. Haley, that his title will be Executive Chairman of Aon focusing on growth and innovation). These interests, among others, may have an influence on the decision of Aon’s and WTW’s directors and executive officers with respect to the scheme, the transaction and the Business Combination Agreement. For more information, including the assumptions used to estimate the value of such interests, please see the sections entitled “The Transaction—Interests of WTW Directors and Executive Officers in the Transaction” and “The Transaction—Interests of Aon Directors and Executive Officers in the Transaction” beginning on pages 109 and 115 of this joint proxy statement, respectively. You should consider these interests in connection with your vote.

In addition, Aon has agreed to appoint four members of the WTW Board to the Aon Board upon the closing of the transaction (including John Haley, the Chief Executive Officer of WTW, who will become the Executive Chairman of Aon, with a focus on growth and innovation), and certain current and former directors and officers of WTW will be entitled to ongoing indemnification and insurance coverage as described in the section entitled “The Business Combination Agreement—Covenants and Agreements—Directors’ and Officers’ Indemnification and Insurance” beginning on page 142 of this joint proxy statement.

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The Aon Board and the WTW Board was each aware of the interests applicable to its directors and executive officers when it determined that the transaction was fair to, and in the best interests of, its company and shareholders.

The opinions of Aon’s and WTW’s respective financial advisors will not reflect changes in circumstances between the signing of the Business Combination Agreement and the closing of the transaction.

The opinions rendered for the benefit of the Aon Board by Credit Suisse and for the benefit of the WTW Board by Goldman Sachs were provided as of their respective dates of delivery to the Aon Board and the WTW Board, respectively. The opinions were based on the financial, economic, market and other conditions as in effect on, and the information made available to Credit Suisse and Goldman Sachs as of, the dates of their respective opinions and do not reflect events occurring after the date of such opinions. Neither the Aon Board nor the WTW Board has obtained an updated opinion as of the date of this joint proxy statement from Credit Suisse or Goldman Sachs, and neither the Aon Board nor the WTW Board expects to obtain an updated opinion prior to the closing of the transaction.

Changes in the operations and prospects of Aon and/or WTW, general market and economic conditions and other factors that may be beyond the control of Aon or WTW, and on which such opinions were based, may have altered the value of Aon and/or WTW or the prices of the Aon Shares and/or the WTW Shares since the date of such opinions, or may alter such values and prices by the time the transaction is completed and, therefore, the opinions do not address the fairness of the scheme consideration from a financial point of view at the time of the special meetings or at the effective time of the transaction. The opinions do not speak as of any date other than the respective dates thereof. The Aon Board’s recommendation that Aon shareholders vote “FOR” all of the proposals being presented at the Aon EGM and the WTW Board’s recommendation that WTW shareholders vote “FOR” all of the proposals being presented at the WTW Court Meeting and the WTW EGM, however, are each made as of the date of this joint proxy statement. For a description of the opinion that Credit Suisse rendered to the Aon Board, see the section entitled “The Transaction—Opinion of Credit Suisse” beginning on page 89 of this joint proxy statement. For a description of the opinion that Goldman Sachs rendered to the WTW Board, see the section entitled “The Transaction—Opinion of Goldman Sachs” beginning on page 97 of this joint proxy statement.

The financial projections are based on various assumptions that may not be realized.

The financial projections set forth in the projections included under the sections entitled “The Transaction—Aon and WTW Forward-Looking Financial Information—Aon Forward-Looking Financial Information” and “The Transaction—Aon and WTW Forward-Looking Financial Information—WTW Forward-Looking Financial Information” beginning on pages 106 and 107 of this joint proxy statement, respectively, were based on assumptions of, and information available to, Aon management and WTW management, respectively, when prepared, and those estimates and assumptions are subject to uncertainties, many of which are beyond Aon’s and/or WTW’s control and may not be realized. Many factors mentioned in this joint proxy statement, including the risks outlined in this “Risk Factors” section and the events or circumstances described under the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 47 of this joint proxy statement, will be important in determining the combined company’s future results. As a result of these contingencies, actual future results may vary materially from the estimates. In view of these uncertainties, the inclusion of financial estimates in this joint proxy statement is not and should not be viewed as a representation that the forecasted results will necessarily reflect actual future results. None of Aon, WTW or their respective affiliates, advisors, officers, directors, partners or representatives can give you any assurance that actual results will not differ materially from the financial projections, and none of them undertake any obligation to update or otherwise revise or reconcile the projections to reflect circumstances existing after the date the projections were generated or to reflect the occurrence of future events, including the impact of Aon, WTW or the combined company of COVID-19.

The financial estimates set forth in the forecasts included under the sections entitled “The Transaction—Aon and WTW Forward-Looking Financial Information—Aon Forward-Looking Financial Information” and “The Transaction—Aon and WTW Forward-Looking Financial Information—WTW Forward-Looking Financial

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Information” beginning on pages 106 and 107 of this joint proxy statement, respectively, were not prepared with a view toward public disclosure or compliance with published guidelines of any regulatory or professional body. Further, any forward-looking statement speaks only as of the date on which it is made and does not take into consideration the impact of events and circumstances occurring after such date, including the impact of COVID-19. Neither Aon nor WTW undertakes any obligation, other than as required by applicable law, to update the financial estimates herein to reflect events or circumstances after the date those financial estimates were prepared or to reflect the occurrence of anticipated or unanticipated events or circumstances. None of Aon’s, WTW’s or any other independent accountants have compiled, examined or performed any procedures with respect to such information, nor have any independent accountants expressed any opinion or any other form of assurance on such information or achievability thereof, and, accordingly, such independent accountants assume no responsibility for, and disclaim any association with, such forward-looking financial information. The audit reports of such independent accountants included or incorporated by reference herein, as applicable, relate exclusively to the historical financial information of the entities named in those reports and do not cover any other information in this joint proxy statement and should not be read to do so. See the sections entitled “The Transaction—Aon and WTW Forward-Looking Financial Information—Aon Forward-Looking Financial Information” and “The Transaction—Aon and WTW Forward-Looking Financial Information—WTW Forward-Looking Financial Information” beginning on pages 106 and 107 of this joint proxy statement, respectively, for more information.

Current Aon shareholders and current WTW shareholders will have a reduced ownership and voting interest after the transaction and will exercise less influence over management.

Aon will issue new Aon Shares to WTW shareholders in the transaction. Immediately following the closing of the transaction, current Aon shareholders and current WTW shareholders are expected to hold approximately 62.8% and 37.2%, respectively, of the outstanding Aon Shares immediately following the closing based on the number of Aon Shares and WTW Shares outstanding as of 5:00 p.m. EDT on June 30, 2020 on a fully diluted basis. Following the closing of the transaction, the Aon Shares held by current Aon shareholders and current WTW shareholders will represent a percentage ownership of the combined company that is smaller than such shareholders’ percentage ownership of Aon and WTW, respectively, before the transaction. As a result of this reduced ownership percentage, current Aon shareholders and current WTW shareholders will have less influence on the management and policies of the combined company than they have as to Aon and WTW prior to the transaction.

In particular, even if all former WTW shareholders voted together on all matters presented to Aon shareholders from time to time following the closing of the transaction, the former WTW shareholders would exercise significantly less influence over Aon after the closing of the transaction relative to their influence over WTW prior to the closing of the transaction, and thus would have a less significant impact on the election of the Aon Board and on the approval or rejection of future Aon proposals submitted to a shareholder vote.

The Aon Shares received by WTW shareholders as a result of the transaction will have different rights from WTW Shares.

Upon the closing of the transaction, WTW shareholders will no longer be shareholders of WTW, and WTW shareholders will become shareholders of Aon. See the section entitled “Comparison of the Rights of Aon Shareholders and WTW Shareholders” beginning on page 177 of this joint proxy statement for a discussion of the rights associated with Aon Shares and WTW Shares.

While the transaction is pending, Aon and WTW will be subject to business uncertainties related to their relationships with employees, clients and suppliers, which could adversely affect Aon’s and/or WTW’s business and operations. These uncertainties could also adversely affect the combined company following the transaction.

Uncertainty about the effect of the transaction on employees, clients and suppliers may have an adverse effect on Aon and WTW and, consequently, on the combined company. These uncertainties may impair Aon’s

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and WTW’s ability to attract, retain and motivate key personnel until the closing of the transaction and for a period of time thereafter, and could cause clients, suppliers and others who deal with Aon and WTW to seek to delay or defer business decisions, to change or terminate existing business relationships with Aon and WTW, or for potential clients to choose other partners instead of Aon or WTW or to take other actions as a result of the transaction that could negatively impact the combined company’s and/or Aon’s or WTW’s respective revenues, earnings and cash flows, as well as the market price of their respective securities. Employee retention may be particularly challenging during the pendency of the transaction because employees may experience uncertainty about their future roles with the combined company. If, despite Aon’s and WTW’s retention efforts, key employees depart because of issues relating to the uncertainty and difficulty of integration or a desire not to remain with the combined company, the combined company’s business could be harmed and its ability to realize the anticipated benefits of the transaction could be adversely affected.

While the transaction is pending, Aon and WTW will be subject to contractual restrictions, which could adversely affect their respective business and operations.

Under the terms of the Business Combination Agreement, Aon and WTW are subject to certain restrictions on the conduct of their respective businesses prior to the closing of the transaction, which may adversely affect the ability of Aon and/or WTW to execute certain of their respective business and operational strategies, including the ability in certain cases to enter into contracts or incur capital expenditures to grow their respective businesses. Such limitations could negatively affect Aon’s and/or WTW’s businesses and operations prior to the closing of the transaction. The adverse effect of the pendency of the transaction could be exacerbated by any delays in completion of the transaction or by the termination of the Business Combination Agreement. Furthermore, the process of planning to integrate two businesses and organizations for the post-transaction period can divert management attention and resources and could ultimately have an adverse effect on Aon and/or WTW.

There can be no assurance that the transaction will not result in a downgrade, suspension or withdrawal of any credit rating assigned by a credit ratings agency to the securities of Aon, WTW and/or the combined company, which may result in an adverse effect on such entity’s business, financial condition, operating results and securities prices.

Credit ratings are not a recommendation to buy, sell or hold any security, and may be revised or withdrawn at any time by the issuing credit ratings agency in its sole discretion. Credit ratings agencies continually review their ratings for the companies that they follow, including Aon, WTW and, following the completion of the transaction, the combined company. Credit ratings agencies may also change their ratings for the securities of the companies that they follow based on their overall view of the relevant industry. A downgrade, suspension or withdrawal, or the announcement of a possible downgrade, suspension or withdrawal, of the credit ratings assigned to the securities of Aon, WTW and/or the combined company, or any anticipated change in such credit ratings, could adversely affect such entity’s business, financial condition, operating results and securities prices.

In addition, credit ratings agencies that currently or may in the future publish ratings for the securities of Aon, WTW and/or the combined company may, from time to time, change the methodologies that they use for analyzing such securities. If such credit ratings agencies were to change their practices and/or methodologies, and such change led to a downgrade, suspension or withdrawal of the credit ratings assigned to such securities, the business, financial condition, operating results and securities prices of the affected entity could be adversely affected.

The effective tax rate that will apply to the combined company is uncertain and may vary from expectations.

There can be no assurance that completion of the scheme will allow the combined company to maintain any particular worldwide effective corporate tax rate. No assurances can be given as to what the combined company’s effective tax rate will be after completion of the scheme because of, among other things, uncertainty regarding the jurisdictions in which the combined company will derive income and the amounts derived thereof and

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uncertainty regarding the tax policies of the jurisdictions in which it operates. The combined company’s actual effective tax rate may vary from expectations and that variance may be material. Additionally, tax laws or their implementation and applicable tax authority practices could change in the future.

The combined company and its subsidiaries will be subject to tax laws of numerous jurisdictions, and the interpretation of those laws is subject to challenge by the relevant governmental authorities.

The combined company will be subject to tax laws and regulations in the United States, Ireland and the numerous other jurisdictions in which the combined company and its subsidiaries will operate. These laws and regulations are inherently complex, and the combined company and its subsidiaries will be obligated to make judgments and interpretations about the application of these laws and regulations to the combined company and its subsidiaries and their operations and businesses. The interpretation and application of these laws and regulations could be challenged by the relevant governmental authorities, which could result in administrative or judicial procedures, actions or sanctions, which could be material.

The IRS may disagree that the transaction is treated as a reorganization.

The transaction is intended to qualify as a “reorganization” within the meaning of Section 368(a) of the Code, referred to as a “Reorganization.” Provided that the transaction so qualifies, a holder of WTW Shares generally will not recognize any gain or loss for U.S. federal income tax purposes on the exchange of such shares for Aon Shares in the transaction, except with respect to any cash received in lieu of fractional Aon Shares. No rulings are intended to be sought from the U.S. Internal Revenue Service, referred to as the “IRS,” with respect to the transaction and there can be no assurance that the IRS or a court will not take a contrary position regarding the tax consequences described herein. If the IRS successfully challenges the treatment of the transaction as a Reorganization, all holders of WTW Shares would recognize any taxable gain or loss for U.S. federal income tax purposes realized upon the exchange of WTW Shares for Aon Shares.

For a further discussion, see the section entitled “Material Tax Consequences of the Transaction—Material U.S. Federal Income Tax Considerations” beginning on page 122 of this joint proxy statement.

Litigation filed against WTW and/or Aon could prevent or delay the completion of the transaction or result in the payment of damages following completion of the transaction.

WTW, Aon and members of the WTW Board currently are and may in the future be parties, among others, to various claims and litigation related to the Business Combination Agreement and the transaction, including putative shareholder class actions. For additional information regarding the pending litigation, see the section entitled “The Transaction—Litigation Relating to the Transaction” beginning on page 119 of this joint proxy statement. Among other remedies, the plaintiffs in such matters are seeking to enjoin the transaction. The results of complex legal proceedings are difficult to predict, and could delay or prevent the transaction from being completed in a timely manner, and could result in substantial costs to Aon and WTW, including, but not limited to, costs associated with the indemnification of their respective directors and officers. The existence of litigation relating to the transaction could impact the likelihood of obtaining the required approvals from either WTW’s or Aon’s shareholders. Moreover, the pending litigation and any future additional litigation could be time consuming and expensive, could divert WTW’s and Aon’s management’s attention away from their regular businesses, and, if any one of these lawsuits is adversely resolved against either WTW or Aon, could have a material adverse effect on WTW’s or Aon’s respective financial condition.

One of the conditions to the closing of the transaction is that no order (whether temporary or permanent) has been issued, promulgated, made, rendered or entered into by any court or other tribunal of competent jurisdiction which restrains, enjoins, makes illegal or otherwise prohibits the consummation of the transaction (excluding certain laws and orders unrelated to the required antitrust clearances and the required regulatory clearances). Consequently, if plaintiffs are successful in obtaining an injunction prohibiting WTW and Aon from completing the transaction on the terms contemplated by the Business Combination Agreement, such an injunction may delay the completion of the transaction in the expected timeframe, or may prevent the transaction from being completed altogether.

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Risks Relating to the Combined Company Following the Transaction

If completed, the transaction may not achieve its intended results.

Aon and WTW entered into the Business Combination Agreement with the expectation that the transaction would result in various benefits, including, among other things, synergies at the combined company, a comprehensive and more innovative product portfolio, diversified growth profile and broad geographic reach. Achieving the anticipated benefits of the transaction is subject to a number of uncertainties, including whether the businesses of Aon and WTW can be integrated in an efficient and effective manner. Failure to achieve, a delay in achieving, or an increase in the costs to achieve, these anticipated benefits, in whole or in part, could result in increased costs or decreases in expected revenues and could adversely affect the combined company’s future business, financial condition, operating results and cash flows. Additionally, if any governmental agencies, in connection with the transaction, require divestitures or place restrictions on the conduct of the combined company’s business after the closing of the transaction, such requirements or restrictions could reduce the anticipated benefits of the transaction.

Aon and WTW may be unable to successfully integrate their operations. Failure to successfully integrate the businesses of Aon and WTW in the expected timeframe may adversely affect the future results of the combined company.

The ability of Aon and WTW to realize the anticipated benefits of the transaction will depend, to a large extent, on the ability to integrate Aon’s and WTW’s business. The combination of two independent businesses is a complex, costly and time-consuming process. As a result, significant management attention and resources will be devoted to integrating the business practices and operations of Aon and WTW. The integration process may disrupt the businesses and, if implemented ineffectively, would preclude realization of the full expected benefits. A failure to meet the challenges involved in integrating the two businesses and to realize the anticipated benefits of the transaction could adversely affect the combined company’s results of operations.

In addition, the overall integration of the businesses may result in material unanticipated problems, expenses, liabilities, competitive responses, loss of client relationships and diversion of management’s attention. The difficulties of combining the operations of the companies include, among others: the diversion of management attention to integration matters; difficulties in achieving anticipated cost savings, synergies, business opportunities and growth prospects from combining the businesses; difficulties in the integration of operations and systems; unanticipated costs, delays and other hardships to integration efforts, including any such costs, delays or hardships, caused by pandemic, epidemic or outbreak of an infectious disease, including COVID-19 and the resulting travel and operations restrictions; difficulties in the assimilation of employees and culture; difficulties in managing the expanded operations of a larger and more complex company; challenges in retaining existing clients and obtaining new clients; and challenges in attracting and retaining key personnel.

Many of these factors will be outside of Aon’s and WTW’s control and any one of them could result in increased costs, decreases in expected revenues and diversion of management’s time and attention, which could materially impact the business, financial condition and results of operations of the combined company. In addition, even if the operations of the businesses of Aon and WTW are integrated successfully, the full benefits of the transaction, including the synergies, cost savings or sales or growth opportunities that are expected, may not be realized within the anticipated time frame or at all. Further, additional unanticipated costs may be incurred in the integration of the businesses of Aon and WTW. All of these factors could decrease or delay the expected accretive effect of the transaction and negatively impact the combined company’s results of operations.

A pandemic, epidemic or outbreak of an infectious disease, including COVID-19, may materially and adversely affect the businesses, results of operations and financial results of Aon, WTW and/or the combined company.

The recent outbreak of COVID-19 in December 2019 has spread throughout the world, including the United States and Europe. The spread of COVID-19 has already affected the global economy and may adversely affect

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the operations and financial results of Aon, WTW and/or the combined company (including their respective ability to manage liquidity) by, among other things, causing a period of business disruptions or shutdowns. Neither Aon nor WTW can currently predict the scope and severity of any potential business disruptions or shutdowns, but if Aon, WTW, the combined company and/or any of the third parties with whom Aon, WTW or the combined company engages were to experience business disruptions or shutdowns, the ability of Aon, WTW and/or the combined company to conduct business in the manner and on the timelines presently planned could be materially and negatively impacted, which could have a material adverse effect on the integration of the businesses and the results of operations and financial condition of Aon, WTW and/or the combined company.

Aon and WTW have incurred and will incur substantial transaction fees and costs in connection with the transaction.

Aon and WTW have incurred and expect to incur a number of non-recurring substantial transaction-related costs associated with the closing of the transaction, combining the operations of the two organizations and achieving desired synergies. These fees and costs will be substantial, and a portion of them will be incurred regardless of whether the transaction closes. Non-recurring transaction costs include, but are not limited to, fees paid to legal, financial and accounting advisors, retention, severance, change in control and other integration-related costs, filing fees and printing costs. Additional unanticipated costs may be incurred in connection with the closing and the integration of the businesses of Aon and WTW. There can be no assurance that the elimination of certain duplicative costs, as well as the realization of other efficiencies related to the integration of the two businesses, will offset the incremental transaction-related costs over time. Thus, any net benefit may not be achieved in the near term, the long term or at all, and these costs could adversely affect the financial conditions and results of operation of Aon and WTW prior to the closing and of the combined company following the closing.

The pro forma financial statements included in this joint proxy statement are based on various assumptions that may not prove to be correct, and they are presented for illustrative purposes only and may not be an indication of the combined company’s financial condition or results of operations following the transaction.

The pro forma financial statements contained in this joint proxy statement are based on various adjustments, assumptions and preliminary estimates and may not be an indication of the combined company’s financial condition or results of operations following the transaction for several reasons. See the section entitled “Unaudited Pro Forma Condensed Combined Financial Information” beginning on page 153 of this joint proxy statement. The actual financial condition and results of operations of the combined company following the transaction may not be consistent with, or evident from, these pro forma financial statements. In addition, the assumptions used in preparing the pro forma financial information may not prove to be accurate, and other factors may affect the combined company’s financial condition or results of operations following the transaction.

Following the transaction, the combined company will have a substantial amount of debt, which could adversely affect its business, financial condition or results of operations and prevent it from fulfilling its debt-related obligations.

Following the transaction, the combined company will have a substantial amount of debt. The combined company’s substantial debt could adversely affect it in a number of ways, including, but not limited to, making it more difficult for the combined company to satisfy its obligations with respect to its debt or to its trade or other creditors, leading a credit ratings agency to downgrade its credit ratings assigned to the combined company, requiring a substantial portion of the combined company’s cash flows from operations and the proceeds of any capital markets offerings or loan borrowings for the payment of interest on the combined company’s debt, increasing the combined company’s vulnerability to changing economic, regulatory and industry conditions, limiting the combined company’s flexibility in planning for or reacting to changes in its business and the industry, limiting the combined company’s ability to pay dividends to its shareholders and limiting the combined company’s ability to borrow additional funds. If the combined company cannot service its indebtedness, it may have to take actions such as selling assets, seeking additional debt or equity or reducing or delaying capital expenditures, strategic acquisitions, investments and alliances.

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Certain Aon and WTW agreements may contain change of control provisions that may be triggered by the transaction and, if not waived, could cause the combined company to lose the benefit of such agreements and incur liabilities and/or replacement costs, which could have an adverse effect on the combined company.

Aon and WTW are each party to, or may become party to after the date hereof, various agreements with third parties, including, among other agreements, certain license agreements, collaboration agreements, business development-related agreements, production and distribution related agreements, financing facilities, hedging arrangements, contracts for the performance of services material to the operations of Aon, WTW and/or their affiliates, and employment agreements that may contain change of control provisions that may be triggered upon the closing of the transaction. In the event that there is such a contract or arrangement requiring a consent or waiver in relation to the transaction, for which such consent or waiver is not obtained, the combined company could lose the benefit of the underlying agreement and incur liabilities or replacement costs, which could have an adverse effect on the operations of the combined company. In addition, the counterparties to such contracts may seek consideration for granting such consents or waivers or may seek to renegotiate the contracts on terms less favorable to Aon, or WTW, as applicable, which could have an adverse effect on the operations of the combined company.

The transaction may not be accretive and may cause dilution to Aon’s earnings per share, which may negatively affect the market price of Aon Shares.

As described and based on the assumptions in the section of this joint proxy statement entitled “The Transaction—Scheme Consideration to WTW Shareholders” beginning on page 67 of this joint proxy statement, based on the number of WTW Shares and WTW equity awards outstanding as of 5:00 p.m. EDT on June 30, 2020, Aon expects to issue approximately 141,249,022 Aon Shares in connection with completion of the transaction (including shares underlying WTW equity awards expected to be outstanding at the effective time, which will be converted into awards with respect to Aon Shares). The issuance of these new Aon Shares could have the effect of depressing the market price of Aon Shares.

In addition, Aon could also encounter additional transaction-related and/or integration-related costs or other factors such as the failure to realize all or a portion of the benefits anticipated in the transaction on a timely basis or at all. All of these factors could cause dilution to Aon’s earnings per share or decrease or delay the expected accretive effect of the transaction and cause a decrease in the market price of Aon Shares.

The market price of Aon Shares may decline in the future as a result of the sale of Aon Shares held by former WTW shareholders or current Aon shareholders.

Based on the number of WTW Shares and WTW equity awards outstanding as of 5:00 p.m. EDT on June 30, 2020, Aon expects to issue approximately 141,249,022 Aon Shares to WTW shareholders in the transaction (including shares underlying WTW equity awards expected to be outstanding at the effective time, which will be converted into awards with respect to Aon Shares). Following their receipt of Aon Shares as scheme consideration, former WTW shareholders may seek to sell the Aon Shares delivered to them. Other Aon shareholders may also seek to sell Aon Shares held by them following, or in anticipation of, completion of the transaction. These sales (or the perception that these sales may occur), coupled with the increase in the outstanding number of Aon Shares, may affect the market for, and the market price of, Aon Shares in an adverse manner.

Risks Relating to Aon’s Business

You should read and consider risk factors specific to Aon’s businesses that may also affect the combined company after the closing of the transaction. These risks are described in Part I, Item 1A of Aon’s Annual Report on Form 10-K for the year ended December 31, 2019, and in Part II, Item 1A of Aon’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, as well as in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement for the location of information incorporated by reference in this joint proxy statement.

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Risks Relating to WTW’s Business

You should read and consider risk factors specific to WTW’s businesses that may also affect the combined company after the closing of the transaction. These risks are described in Part I, Item 1A of WTW’s Annual Report on Form 10-K for the year ended December 31, 2019, and in Part II, Item 1A of WTW’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, as well as in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement for the location of information incorporated by reference in this joint proxy statement.

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This joint proxy statement contains certain statements that are forward-looking, as that term is defined in the Private Securities Litigation Reform Act of 1995, including statements related to Aon’s and/or WTW’s ability to manage its respective businesses and liquidity during and after the COVID-19 pandemic. Forward-looking statements are prospective in nature and are not based on historical facts, but rather on current expectations of Aon and WTW management about future events. Forward-looking statements can often, but not always, be identified by the use of words such as “plans,” “expects,” “is subject to,” “budget,” “scheduled,” “estimates,” “forecasts,” “potential,” “continue,” “intends,” “anticipates,” “believes” or variations of such words, and statements that certain actions, events or results “may,” “could,” “should,” “would,” “might” or “will” be taken, occur or be achieved.

Although Aon and WTW management, as applicable, believe that the expectations reflected in these forward-looking statements are reasonable, it can give no assurance that these expectations will prove to be correct. By their nature, forward-looking statements involve risks and uncertainties because they relate to events and depend on circumstances that will occur in the future. There are a number of factors that could cause actual results and developments to differ materially from those expressed or implied by the forward-looking statements. Such factors include, but are not limited to; the possibility that the transaction will not be consummated; failure to obtain necessary shareholder and antitrust, competition and other regulatory approvals (without the imposition of material remedies or at all), or to satisfy any of the other conditions to the closing of the transaction; adverse effects on the market price of Aon and/or WTW securities and on Aon’s and/or WTW’s operating results for any reason, including, without limitation, because of the failure to consummate the transaction; the impact of COVID-19 on Aon’s and/or WTW’s operations and future plans; the failure to realize the expected benefits of the transaction (including anticipated revenue and growth synergies); the failure to effectively integrate the combined companies following consummation of the transaction; negative effects of an announcement of the transaction; changes in global, political, economic, business, competitive, market and regulatory forces; future exchange and interest rates; changes in tax laws, regulations, rates and policies; future business acquisitions or disposals; negative effects of any announcement relating to the consummation of or failure to consummate the transaction on the market price of Aon and/or WTW securities; significant transaction and integration costs or difficulties in connection with the transaction and/or unknown or inestimable liabilities; pending and/or potential future litigation associated with the transaction; the potential impact of this joint proxy statement or consummation of the transaction on relationships, including with suppliers, customers, clients, employees and regulators; and general economic, business and political conditions (including any epidemic, pandemic or disease outbreak) that affect the combined companies following the consummation of the transaction.

The factors identified above are not exhaustive. Aon, WTW and their subsidiaries operate in a dynamic business environment in which new risks may emerge frequently. Other unknown or unpredictable factors could also cause actual results and developments to differ materially from those expressed or implied by the forward-looking statements. Forward-looking statements should therefore be construed in the light of such factors. You are cautioned not to place undue reliance on any forward-looking statements, which speak only as of the date made.

Further information concerning Aon and its businesses, including economic, competitive, governmental, regulatory, technological and other factors that could materially affect Aon’s results of operations and financial condition, is contained in Aon’s filings with the SEC. See Aon’s Annual Report on Form 10-K for the year ended December 31, 2019 and Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, filed with the SEC on February 14, 2020 and May 1, 2020, respectively, and additional documents filed by Aon with the SEC after the date of this joint proxy statement and prior to the Aon EGM, the contents of which are incorporated by reference into this joint proxy statement, for a further discussion of these and other risks and uncertainties applicable to Aon’s businesses.

Further information concerning WTW and its businesses, including economic, competitive, governmental, regulatory, technological and other factors that could materially affect WTW’s results of operations and financial

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condition, is contained in WTW’s filings with the SEC. See WTW’s Annual Report on Form 10-K for the year ended December 31, 2019, and Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, filed with the SEC on February 26, 2020 and April 30, 2020, respectively, and additional documents filed by WTW with the SEC after the date of this joint proxy statement and prior to the WTW Court Meeting and the WTW EGM, the contents of which are incorporated by reference into this joint proxy statement, for a further discussion of these and other risks and uncertainties applicable to WTW’s businesses.

Any forward-looking statements in this joint proxy statement are based upon information available as of the date of this joint proxy statement which, while believed to be true when made, may ultimately prove to be incorrect. Other than in accordance with legal or regulatory obligations, neither Aon nor WTW is under any obligation, and each expressly disclaims any intention or obligation, to update or revise any forward-looking statement, whether as a result of new information, future events or otherwise. All subsequent written and oral forward-looking statements attributable to Aon, WTW and/or any person acting on behalf of any of them are expressly qualified in their entirety by the foregoing paragraphs, and the information contained on any websites referenced in this joint proxy statement is not incorporated by reference into this joint proxy statement.

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SELECTED HISTORICAL CONSOLIDATED DATA OF AON

The selected historical consolidated financial data presented below as of December 31, 2019 and 2018 and for the years ended December 31, 2019, 2018 and 2017 has been derived from Aon’s audited consolidated financial statements included in Aon’s Annual Report on Form 10-K for the year ended December 31, 2019 (except for Item 8 therein to the extent superseded by Aon’s Current Report on Form 8-K filed with the Commission on April 1, 2020), each of which is incorporated by reference herein. The selected historical consolidated financial data presented below as of December 31, 2017 and 2016 and for the years ended December 31, 2016 and 2015 has been derived from Aon’s audited financial statements included in Aon’s Annual Report on Form 10-K for the year ended December 31, 2017, which is not incorporated by reference herein. The selected historical consolidated financial data presented below as of December 31, 2015 has been derived from Aon’s audited financial statements included in Aon’s Annual Report on Form 10-K for the year ended December 31, 2016, which is not incorporated by reference herein. The selected historical consolidated financial data presented below as of March 31, 2020 and for the three months ended March 31, 2020 and 2019 has been derived from the unaudited consolidated financial statements included in Aon’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, which is incorporated by reference herein. The selected historical consolidated financial data presented below as of March 31, 2019 has been derived from the unaudited consolidated financial statements included in Aon’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2019, which is not incorporated by reference herein.

You should read the following information in conjunction with Aon’s consolidated financial statements and related notes and other financial information incorporated by reference in this joint proxy statement. Historical results are not necessarily indicative of any results to be expected in the future. See the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement.

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SELECTED HISTORICAL CONSOLIDATED DATA OF WTW

The selected historical consolidated financial data presented below for the years ended December 31, 2019, 2018 and 2017 and as of December 31, 2019 and 2018 has been derived from the audited consolidated financial statements of WTW included in WTW’s Annual Report on Form 10-K for the year ended December 31, 2019, which is incorporated by reference herein. During 2019 and 2018, WTW adopted ASC 842, Leases and ASC 606, Revenue from Contracts with Customers, respectively. Financial information presented for years prior to the respective adoptions has not been adjusted in accordance with the provisions of those new standards. The selected historical financial data presented below for the year ended December 31, 2016 and as of December 31, 2017 and 2016 has been derived from the audited consolidated financial statements of WTW included in WTW’s Annual Report on Form 10-K for the year ended December 31, 2017, which is not incorporated herein. The selected historical financial data presented below as of and for the year ended December 31, 2015 has been derived from the audited consolidated financial statements of Willis Group Holdings Public Limited Company, predecessor to WTW, prior to the merger with Towers Watson & Co., completed in 2016, referred to as the “Merger,” included in Willis Group Holdings Public Limited Company’s Annual Report on Form 10-K for the year ended December 31, 2015, which is not incorporated herein, and is presented with adjustment for the reverse stock split on January 4, 2016. The Merger affects the comparability of this data for the year ended December 31, 2015. In addition, WTW has reclassified certain prior period amounts in 2016 and 2015 to conform to current period presentation due to the adoption of certain updated accounting standards requiring retrospective application. The selected historical financial data as of March 31, 2020 and for the three months ended March 31, 2020 and 2019 have been derived from the unaudited condensed consolidated financial statements in WTW’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2020, which is incorporated by reference herein. The selected historical consolidated balance sheet data as of March 31, 2019 has been derived from the unaudited condensed consolidated financial statements contained in WTW’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2019, which has not been incorporated by reference herein.

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You should read the following information in conjunction with WTW’s consolidated financial statements and related notes and other financial information incorporated by reference in this joint proxy statement. Historical results are not necessarily indicative of any results to be expected in the future. See the section entitled “Where You Can Find More Information” beginning on page 191 of this joint proxy statement.

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SELECTED UNAUDITED COMBINED PRO FORMA FINANCIAL DATA

The following selected unaudited combined pro forma financial data, referred to as the “Selected Pro Forma Data,” give effect to the transaction. The Selected Pro Forma Data have been prepared using the acquisition method of accounting, based on the historical financial information of Aon and WTW. The acquisition method of accounting under ASC 805-20-30-1 requires that the acquirer measure the identifiable assets acquired, the liabilities assumed, and any noncontrolling interest in the acquiree at their acquisition-date fair values. Under the acquisition method of accounting, assets acquired and liabilities assumed are generally recorded at their respective fair values as of the date the acquisition is completed.

The selected unaudited pro forma condensed combined statement of financial position as of March 31, 2020 gives effect to the transaction as if it had been completed on March 31, 2020, and the unaudited pro forma condensed combined statements of income for the three months ended March 31, 2020 and the year ended December 31, 2019 give effect to the transaction as if it had been completed on January 1, 2019. The historical consolidated financial information has been adjusted to give effect to pro forma events that are (i) directly attributable to closing the transaction, (ii) factually supportable, and (iii) with respect to the pro forma condensed combined statements of income, expected to have continuing impact on the results of the combined company.

The Selected Pro Forma Data have been derived from, and should be read in conjunction with, the more detailed unaudited pro forma condensed combined financial information appearing elsewhere in this joint proxy statement and the accompanying notes to the pro forma statements. In addition, the pro forma statements were based on, and should be read in conjunction with, the historical consolidated financial statements and related notes of both Aon and WTW for the applicable periods, which have been incorporated in this joint proxy statement by reference. See the sections entitled “Where You Can Find More Information” and “Unaudited Pro Forma Condensed Combined Financial Information” beginning on pages 191 and 153 in this joint proxy statement, respectively, for additional information. The Selected Pro Forma Data have been presented informational purposes only and are not necessarily indicative of the financial position or results of operations that the combined company would have realized had the transaction been completed on the dates indicated, nor are they meant to be indicative of any anticipated or future financial position or results of operations that the combined company will experience following the transaction. Also, as explained in more detail in the accompanying notes to the pro forma statements, the preliminary fair values of assets acquired and liabilities assumed reflected in the Selected Pro Forma Data are subject to adjustment and may change as additional information becomes available and such changes could be material.

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PART 1—THE TRANSACTION AND THE SPECIAL MEETINGS

THE SPECIAL MEETINGS OF WTW SHAREHOLDERS

Overview

This joint proxy statement is being provided to WTW shareholders as part of a solicitation of proxies by the WTW Board for use at the special meetings of WTW shareholders referred to below and at any adjournments thereof. This joint proxy statement is being furnished to WTW shareholders on or about July 8, 2020.

Date, Time, and Place of the Special Meetings

The WTW Court Meeting will be held on August 26, 2020 at 10:30 a.m., EDT, at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131 and Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland. The WTW EGM will be held on August 26, 2020 at 11:00 a.m., EDT, or, if the WTW Court Meeting has not concluded by 11:00 a.m., EDT, as soon as possible after the conclusion or adjournment of the WTW Court Meeting at Willis Towers Watson Public Limited Company, 1450 Brickell Avenue, Suite 1600, Miami, Florida 33131 and Matheson, 70 Sir John Rogerson’s Quay, Dublin 2, Ireland.

Attendance and Voting

Attendance at the WTW Court Meeting and the WTW EGM is limited to WTW shareholders at the WTW Voting Record Time. If your shares are held in an account with a broker, bank or other nominee, this institution is considered the shareholder of record and you are considered the “beneficial shareholder” of those shares. In this case, your broker or bank (or its agent) or other nominee has forwarded the proxy materials and separate voting instructions to you. Because you are not the shareholder of record, you may not vote your shares in person at the WTW special meetings unless you obtain a valid proxy from the broker, bank or other nominee that holds your shares, giving you the right to vote the shares in person at the meetings. As the beneficial owner of the shares, you have the right to direct your broker, bank or other nominee how to vote your shares by following the voting instructions provided to you with the proxy materials. For admission to the meetings, shareholders of record must bring proof of identification and address. Those who have beneficial ownership of shares held by a bank, brokerage firm or other nominee should bring account statements or letters from their banks, brokers or other nominees showing that they owned WTW Shares as of the WTW Voting Record Time. Completion and return of a form of proxy will not preclude a WTW shareholder from attending and voting in person at the WTW Court Meeting or the WTW EGM, or any adjournments thereof, if that shareholder wishes to do so. Any alteration to the form of proxy must be initialed by the person who signs it.

Irish law requires WTW to hold a physical meeting for the WTW Court Meeting and the WTW EGM. In light of COVID-19, we encourage WTW shareholders to vote by proxy prior to 11:59 p.m. EDT on August 25, 2020 as described in this joint proxy statement. WTW asks that, in considering whether to attend such meetings in person, WTW shareholders follow public health and travel guidelines with respect to COVID-19, including as applicable to Ireland and the United States. Those guidelines may restrict or prevent any WTW shareholder from attending such meetings in person. WTW strongly encourages WTW shareholders not to attend such meetings in person if they are experiencing any of the described COVID-19 symptoms. WTW shareholders attending the WTW special meetings in person are also requested to follow the hygiene instructions consistent with applicable public health guidelines, including washing or disinfecting hands upon arrival at such meetings. WTW may take additional precautionary measures in relation to the WTW special meetings in response to further developments in the COVID-19 outbreak. WTW will be obliged to comply with any legal restrictions that are imposed as a consequence of COVID-19 and that affect such meetings, which may include preventing or restricting access to such meetings. WTW also intends to comply with any applicable public health and travel guidelines, which may affect the WTW special meetings. Depending on concerns about and developments relating to the COVID-19 outbreak, the WTW Board could determine to change the date, time, location or format of the WTW special

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meetings, subject to Irish legal requirements. In the event WTW determines it is necessary or appropriate to take additional steps regarding how the WTW special meetings will be conducted, WTW will announce such determinations in advance in accordance with applicable legal requirements, and details will be posted on WTW’s website and filed with the U.S. Securities and Exchange Commission.

Record Date, Shares Entitled to Vote

Only holders of WTW Shares as of the WTW Voting Record Time, which is 5:00 p.m. EDT on June 30, 2020, the record date for the special meetings, will be entitled to notice of, and to vote at the special meetings or any adjournments thereof. At the WTW Voting Record Time, there were 128,762,994 WTW Shares outstanding, held by 1,199 holders of record. Voting will be by poll, and each outstanding WTW Share is entitled to one vote on each proposal and any other matter properly coming before the special meetings, subject to certain exceptions for Aon and its affiliates.

Quorum

A quorum will exist with respect to each matter to be considered at the WTW Court Meeting and the WTW EGM if the holders of WTW Shares representing at least 50% of the WTW Shares issued and outstanding at the WTW Voting Record Time, each being a holder of WTW Shares as of the WTW Voting Record Time, a proxy for a holder of WTW Shares as of the WTW Voting Record Time or a duly authorized representative of a corporate holder of WTW Shares as of the WTW Voting Record Time, are present in person or by proxy and entitled to vote, provided however that if a class of shareholders has only one shareholder, then one shareholder present in person or by proxy shall constitute the necessary quorum. WTW Shares held in “street name” will be counted as present for the purpose of determining the existence of a quorum at the WTW Court Meeting and the WTW EGM so long as a shareholder has given the bank, broker or other nominee voting instructions on at least one of the proposals or resolutions, as applicable, brought before the meeting. Abstentions, though counted for the purposes of determining that a quorum is present, will not be counted as votes cast and therefore will have no effect on the approval of the proposals or resolutions, as applicable.

WTW Share Ownership and Voting by WTW Directors and Officers

As of 5:00 p.m. EDT on June 30, 2020, WTW directors and executive officers had the right to vote approximately 466,576 WTW Shares at the WTW special meetings, representing approximately 0.36% of the WTW Shares entitled to vote at each of such meetings. It is expected that all WTW directors and executive officers will vote “FOR” each of the proposals at the WTW Court Meeting and “FOR” each of the proposals at the WTW EGM. Pursuant to their irrevocable undertakings, all WTW directors have agreed to vote their WTW Shares “FOR” the proposals at the WTW Court Meeting and the WTW EGM, subject to certain exceptions. See the section entitled “Director’s Irrevocable Undertakings” beginning on page 152 of this joint proxy statement.

Proposals

WTW Court Meeting: WTW shareholders (excluding Aon and its affiliates, to the extent they hold WTW Shares) are being asked to consider and vote on a proposal at the WTW Court Meeting to approve the scheme of arrangement.

WTW EGM: WTW shareholders (including Aon and its affiliates, to the extent they hold WTW Shares) are also being asked to consider and vote on a proposal at the WTW EGM to approve the scheme of arrangement, in addition to certain other proposals as set forth in the resolutions described below.

The transaction is conditioned on approval of resolutions 1 and 2.

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The transaction is not conditioned on approval of the following resolutions:

Vote Required; Recommendation of the WTW Board

WTW Court Meeting

Proposal to approve the scheme of arrangement: WTW shareholders are being asked to vote on a proposal to approve the scheme at both the WTW Court Meeting and the WTW EGM. The vote required for such proposal is different at each of the meetings, however.

As set out in full under the section entitled “Part 2—Explanatory Statement—Consents and Special Meetings” beginning on page 196 of this joint proxy statement, in order for the resolution at the special Court-ordered meeting to pass, those voting to approve the scheme must: (a) represent a simple majority (being more than 50%) in number of the WTW shareholders of record as of the WTW Voting Record Time, present and voting (in person or by proxy), and (b) represent 75% or more in value of the WTW Shares held by such holders, as of the WTW Voting Record Time, present and voting (in person or by proxy).

Because the vote required to approve the proposal at the special Court-ordered meeting is based on votes properly cast at the meeting, and because abstentions are not considered votes properly cast, abstentions, along with failures to vote, will have no effect on the approval of such proposal.

The transaction is conditioned on approval of the scheme at the special Court-ordered meeting.

The WTW Board recommends that WTW shareholders vote “FOR” the proposal to approve the scheme at the WTW Court Meeting.

In considering the recommendation of the WTW Board, you should be aware that certain WTW directors and executive officers have interests in the transaction that are in addition to, or different from, the interests they might have as WTW shareholders generally. See the section entitled “The Transaction—Interests of WTW Directors and Executive Officers in the Transaction” beginning on page 109 of this joint proxy statement.

It is important that, for the WTW Court Meeting, as many votes as possible are cast so that the Irish High Court may be satisfied that there is a fair representation of the opinion of Scheme Shareholders as of the WTW Voting Record Time when it is considering whether to sanction the scheme. You are therefore strongly urged to complete and return your proxy card for the WTW Court Meeting as soon as possible.

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WTW EGM

Set forth below is a table summarizing certain information with respect to the resolutions to be voted on at the WTW EGM:

At the WTW EGM, the requisite approval of each of the resolutions depends on whether it is (i) an “ordinary resolution” (the Scheme Approval Resolution, the Compensation Resolution and the Adjournment Resolution), which requires the approval of at least a majority of the votes cast by the holders of WTW Shares present and voting, either in person or by proxy, or (ii) a “special resolution” (the Constitution Amendment Resolution), which requires the approval of at least 75% of the votes cast by the holders of WTW Shares present and voting, either in person or by proxy.

For all the resolutions, because the votes required to approve such resolutions are based on votes properly cast at the WTW EGM, and because abstentions are not considered votes properly cast, abstentions, along with failures to vote, will have no effect on the approval of the resolutions.

As of 5:00 p.m. EDT on June 30, 2020, WTW directors and executive officers had the right to vote approximately 466,576 WTW Shares at the WTW special meetings, representing approximately 0.36% of the WTW Shares entitled to vote at each of such meetings. It is expected that all WTW directors and executive officers will vote “FOR” each of the proposals at the WTW Court Meeting and “FOR” each of the proposals at the WTW EGM. Pursuant to their irrevocable undertakings, all WTW directors have agreed to vote their WTW Shares “FOR” the proposals at the WTW Court Meeting and the WTW EGM, subject to certain exceptions. See the section entitled “Director’s Irrevocable Undertakings” beginning on page 152 of this joint proxy statement.

The WTW Board recommends that WTW shareholders vote “FOR” the proposals to approve each of the resolutions.

In considering the recommendation of the WTW Board, you should be aware that certain WTW directors and executive officers have interests in the transaction that are in addition to, or different from, the interests they might have as WTW shareholders generally. See the section entitled “The Transaction—Interests of WTW Directors and Executive Officers in the Transaction” beginning on page 109 of this joint proxy statement.

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Voting your WTW Shares

WTW Shares held directly in your name as the shareholder of record as of the WTW Voting Record Time, may be voted in person at the WTW Court Meeting and the WTW EGM. If you choose to attend either or both WTW special meetings in person, you will need to bring proof of identification and address.

If you are a WTW shareholder of record as of the WTW Voting Record Time, you will receive two proxy cards (one for the WTW Court Meeting and one for the WTW EGM). You may vote your shares in one of the following ways:

If your shares are held through a WTW employee share plan, you must vote such shares prior to 11:59 p.m. EDT on August 23, 2020. You should contact the trustee of your plan for additional information on voting your shares held through a WTW employee share plan.

Voting on Proxies; Incomplete Proxies

If you own shares in your own name, you are considered, with respect to those shares, the “shareholder of record.” If your shares are held in a stock brokerage account or by a bank or other nominee, you are considered the beneficial owner of shares held in “street name.” If you are a WTW shareholder of record you may use the enclosed proxy cards to tell the persons named as proxies how to vote your shares. If you are a WTW shareholder of record, the shares listed on your proxy cards will include, if applicable, shares held in a book-entry account with WTW’s transfer agent, Computershare Trust Company N.A.

WTW shareholders of record as of the WTW Voting Record time may vote by proxy or in person at the WTW EGM or the WTW Court Meeting. WTW recommends that you submit your proxy even if you plan to attend the WTW EGM or the WTW Court Meeting in person. If you vote by proxy, you may change your vote, among other ways, if you attend and vote at the WTW EGM and WTW Court Meeting. Completion and return of a form of proxy will not preclude a WTW shareholder from attending and voting in person at the WTW Court Meeting or the WTW EGM, or any adjournments thereof, if that WTW shareholder wishes to do so. Any alteration to the form of proxy must be initialed by the person who signs it.

If you properly sign, date, mark and return your proxy card or voting instruction form, your shares will be voted in accordance with your instructions. The named proxies will vote all shares at the WTW Court Meeting or the WTW EGM for which proxies have been properly submitted and not revoked. If you sign and return your proxy card or voting instruction form appointing the named proxies as your proxy but do not mark your card to tell the proxy how to vote on a particular proposal, then your shares will be voted “FOR” such proposal.

WTW shareholders of record may also vote over the internet or by telephone by 11:59 p.m., EDT, on August 25, 2020. Voting instructions are printed on the proxy card or voting instruction form you received, if available. Either method of submitting a proxy will enable your shares to be represented and voted at the WTW Court Meeting and the WTW EGM.

Giving a proxy means that a WTW shareholder of record authorizes the persons named in the enclosed proxy card or voting instruction form to vote its shares at the WTW Court Meeting and the WTW EGM in the manner it directs. A WTW shareholder may also vote by proxy or in person at the WTW Court Meeting and the

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WTW EGM. If you hold WTW Shares in your name as a registered WTW shareholder, to submit a proxy, you may use one of the following methods:

WTW requests that WTW shareholders vote over the internet, by telephone or by completing and signing the accompanying proxy and returning it to WTW as soon as possible in the enclosed postage-paid envelope. When the accompanying proxy is returned properly executed and not later revoked, the WTW Shares represented by it will be voted at the WTW Court Meeting and the WTW EGM in accordance with the instructions contained on the proxy card.

If you sign and return your proxy or voting instruction card without indicating how to vote on the WTW proposals, the WTW Shares represented by your proxy will be voted “FOR” each such proposal.

EVERY WTW SHAREHOLDER’S VOTE IS IMPORTANT. ACCORDINGLY, EACH WTW SHAREHOLDER SHOULD VOTE, WHETHER OR NOT THE WTW SHAREHOLDER PLANS TO ATTEND THE WTW COURT MEETING AND THE WTW EGM IN PERSON.

Voting WTW Shares Held in Street Name

If your shares are held in “street name,” you should follow the instructions provided by your bank, broker or other nominee in order to instruct them how to vote such shares. As the beneficial owner of the shares, you have the right to direct your broker, bank or other nominee how to vote your shares by following the voting instructions provided to you with the proxy materials. The bank, broker or other nominee, as applicable, may have an earlier deadline by which you must provide instructions to it as to how to vote shares, so you should carefully read the materials provided to you by your bank, broker or other nominee. Because you are not the shareholder of record, you may not vote your shares in person at the WTW Court Meeting or WTW EGM unless you obtain a valid proxy from the broker, bank or other nominee that holds your WTW Shares, giving you the right to vote the shares in person at the meeting. To request a legal proxy, please contact your bank, broker or other nominee holder of record. It is suggested you do so in a timely manner to ensure receipt of your legal proxy prior to the applicable WTW special meeting.

Brokers do not have discretionary authority to vote on any of the proposals at either of the special meetings. As a result, if you hold your shares in a stock brokerage account or if your shares are held by a bank or nominee, your bank, broker or other nominee will not vote your shares if you do not provide your bank, broker or other nominee with a signed voting instruction form with respect to your shares. Therefore, you should instruct your bank, broker or other nominee to vote your shares by following the directions your bank, broker or other nominee provides.

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In order to attend either or both WTW special meetings, you will need to bring proof of identification and address, as well as proof of share ownership. A recent brokerage statement or a letter from a bank or broker are examples of proof of ownership.

Revoking your Proxy

If you are a WTW shareholder of record, you may revoke your proxy before it is voted at the WTW Court Meeting or before your proxy is voted at the WTW EGM by:

Attendance at either special meeting will not, in and of itself, revoke a proxy or change your voting instructions; you must vote by ballot at the applicable meeting to change your vote.

If your shares are held in “street name” by a bank, broker or other nominee, you should follow the instructions of your bank, broker or other nominee regarding the revocation of proxies.

Costs of Solicitation

Aon and WTW will share equally the cost of soliciting proxies from WTW shareholders in connection with the WTW Court Meeting and the WTW EGM.

WTW will, through its proxy solicitation firm, solicit proxies by mail. WTW will make arrangements with brokerage houses and other custodians, nominees and fiduciaries for forwarding proxy solicitation material to the beneficial owners of WTW Shares held of record by those persons and will reimburse them for their reasonable out-of-pocket expenses incurred in forwarding such proxy solicitation materials.

WTW has engaged a professional proxy solicitation firm, Innisfree, to assist in soliciting proxies for a fee of up to $75,000, as well as reasonable and documented out-of-pocket expenses. WTW also has agreed to indemnify Innisfree against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

Other Business

WTW is not aware of any other business to be acted upon at either of the special meetings. If, however, other matters are properly brought before the special meetings, the named proxies will have discretion to vote or act on those matters according to their best judgment and they intend to vote the WTW Shares as the WTW Board may recommend.

Adjournment

Any adjournment of the WTW Court Meeting will result in an adjournment of the WTW EGM.

Assistance

If you need assistance in completing your proxy cards or have questions regarding the WTW special meetings, please contact Innisfree, the proxy solicitation agent for WTW, by mail at 501 Madison Avenue, 20th Floor, New York, New York 10022 or shareholders may call toll free at 1-888-750-5884 or banks and brokers may call collect at 1-212-750-5833.

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THE EXTRAORDINARY GENERAL MEETING OF AON SHAREHOLDERS

Overview

This joint proxy statement is being provided to Aon shareholders as part of a solicitation of proxies by the Aon Board for use at the Aon EGM and at any adjournment thereof. This joint proxy statement is being furnished to Aon shareholders on or about July 8, 2020 to provide them with information they need to be able to vote or instruct their vote to be cast at the Aon EGM.

Date, Time and Place

The Aon EGM has been convened for 10:00 a.m., CDT (11:00 a.m., EDT), on August 26, 2020 at 200 East Randolph Street, Chicago, Illinois 60601, United States and, at the same time, Arthur Cox, Ten Earlsfort Terrace, Dublin 2, D02 T380, Ireland (where such participation in Ireland shall be by technological means).

As part of our precautions regarding the recent outbreak of COVID-19, we are sensitive to the public health and travel concerns that Aon shareholders may have, as well as any protocols that governmental entities may impose. Accordingly, we have made arrangements to enable persons to attend the Aon EGM virtually via the internet. The virtual attendance does not extend to voting at the Aon EGM. Irish law requires Aon to hold a physical meeting for the Aon EGM. In light of COVID-19, Aon strongly encourages Aon shareholders not to attend the Aon EGM in person, but to vote their Aon Shares in advance via the internet, by telephone, or by completing, signing and returning a form of proxy or voting instruction form, and, if you wish to hear the proceedings and ask questions, to do so virtually, in each case as described under the sections entitled “The Extraordinary General Meeting of Aon Shareholders—Voting Aon Shares Held by Shareholders of Record” and “The Extraordinary General Meeting of Aon Shareholders—Voting Aon Shares Held in Street Name” beginning on pages 64 and 65 of this joint proxy statement, respectively.

Attendance

Attendance at the Aon EGM is limited to Aon shareholders at the Aon Voting Record Time. If you are the beneficial owner of Aon Shares but not the shareholder of record of such Aon Shares (for example, if your Aon Shares are held in “street name” by a bank, broker or other nominee), and you would like to attend the Aon EGM, you will also need proof of your ownership of Aon Shares as of the Aon Voting Record Time. A recent brokerage statement or a letter from a bank or broker are examples of ownership. You will not be permitted to vote in person at the Aon EGM unless you first obtain a legal proxy issued in your name from the record owner and present it to the inspector of election with your ballot at the Aon EGM. To request a legal proxy, contact your bank, broker or other nominee of record. It is suggested you do so in a timely manner to ensure receipt of your legal proxy prior to the Aon EGM. Each Aon shareholder may be asked to provide a valid picture identification, such as a driver’s license or passport, and proof of ownership of his or her Aon Shares as of the Aon Voting Record Time. The use of cell phones, smartphones, pagers, recording and photographic equipment will not be permitted at the Aon EGM.

As part of our precautions regarding the recent outbreak of COVID-19, we are sensitive to the public health and travel concerns that Aon shareholders may have, as well as any protocols that governmental entities may impose. Accordingly, we have made arrangements to enable persons to attend the Aon EGM virtually via the internet. The virtual attendance does not extend to voting at the Aon EGM. Irish law requires Aon to hold a physical meeting for the Aon EGM. In light of COVID-19, we strongly encourage Aon shareholders not to attend the Aon EGM in person, but to vote their Aon Shares in advance via the internet, by telephone, or by completing, signing and returning a form of proxy or voting instruction form, in each case as described in this joint proxy statement. Aon asks that, in considering whether to attend the Aon EGM in person, Aon shareholders follow public health and travel guidelines with respect to COVID-19, including as applicable to Ireland. Those guidelines may restrict or prevent any Aon shareholder from attending the Aon EGM in person. Aon shareholders attending the Aon EGM in person are also requested to follow the hygiene instructions consistent with applicable public health guidelines, including washing or disinfecting hands upon arrival at the Aon EGM. Aon may take additional precautionary measures in relation to the Aon EGM in response to further developments

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in the COVID-19 outbreak. Aon will be obliged to comply with any legal restrictions that are imposed as a consequence of COVID-19 and that affect the Aon EGM, which may include preventing or restricting access to the Aon EGM. Aon also intends to comply with any public health and travel guidelines, which may affect the Aon EGM. Depending on concerns about and developments relating to the COVID-19 outbreak, the Aon Board could determine to change the date, time, location or format of the Aon EGM, subject to Irish legal requirements. In the event Aon determines it is necessary or appropriate to take additional steps regarding how the Aon EGM will be conducted, we will announce such determinations in advance in accordance with applicable legal requirements, and details will be posted on our website and filed with the U.S. Securities and Exchange Commission.

Proposals

Aon shareholders are also being asked to consider and vote on proposals to:

Record Date, Outstanding Ordinary Shares; Shares Entitled to Vote

All holders of record of Aon Shares as of the Aon Voting Record Time, which is 5:00 p.m., EDT, on June 30, 2020, will be entitled to receive notice of, and to vote at, the Aon EGM or any adjournments thereof. As of the Aon Voting Record Time, there were 231,532,083 Aon Shares outstanding, held by 392 holders of record. Voting will be by poll, and each outstanding Aon Share is entitled to one vote on each proposal and any other matter properly coming before the Aon EGM.

Quorum

A quorum will exist with respect to each matter to be considered at the Aon EGM if the holders of Aon Shares representing a majority of the Aon Shares issued and outstanding as of the Aon Voting Record Time are present in person or by proxy and entitled to vote. While Aon does not currently hold any Aon Shares in treasury, such Aon Shares would not be included in the calculation of the number of Aon Shares present at the Aon EGM for the purpose of determining a quorum. Aon’s inspector of election intends to treat as “present” for these purposes Aon shareholders who have submitted properly executed or transmitted proxies that are marked “abstain.” Aon’s inspector of election also intends to treat as “present” shares held in “street name” by brokers so long as an Aon shareholder has given its bank, broker or other nominee voting instructions on at least one proposal to come before the Aon EGM.

Aon Share Ownership and Voting by Aon Directors and Officers

As of 5:00 p.m. EDT on June 30, 2020 Aon directors and executive officers had the right to vote approximately 2,298,921 Aon Shares, representing approximately 0.99% of the Aon Shares entitled to vote at the Aon EGM. It is expected that all Aon directors and executive officers who are also Aon shareholders will vote “FOR” the proposal to approve the issuance of the aggregate scheme consideration pursuant to the transaction, and “FOR” the proposal to approve any motion by the chair of the Aon EGM to adjourn the Aon EGM, or any adjournments thereof, to another time and place if necessary or appropriate to solicit additional proxies if there are insufficient votes at the time of the Aon EGM to approve the other resolution set out above. Pursuant to their irrevocable undertakings, all Aon directors have agreed to vote their Aon Shares “FOR” the proposals at the Aon EGM, subject to certain exceptions. See the section entitled “Director’s Irrevocable Undertakings” beginning on page 152 of this joint proxy statement.

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Vote Required; Recommendation of the Aon Board

Set forth below is a table summarizing certain information with respect to the resolutions to be considered and voted on at the Aon EGM.

Each of the resolutions to be considered at the Aon EGM is an “ordinary resolution,” the approval of which requires the approval of at least a majority of the votes cast by the holders of Aon Shares present and voting, either in person or by proxy.

Because the votes required to approve each of the resolutions are based on votes properly cast at the Aon EGM, and because abstentions are not considered votes properly cast, abstentions, along with failures to vote, will have no effect on the approval of the resolutions.

The Aon Board recommends that Aon shareholders vote “FOR” the proposals to approve each of the resolutions.

In considering the recommendations of the Aon Board described above, you should be aware that certain Aon directors and executive officers have interests in the transaction that are in addition to, or different from, the interests they might have as Aon shareholders generally. See the section entitled “The Transaction—Interests of Aon Directors and Executive Officers in the Transaction” beginning on page 115 of this joint proxy statement.

Voting Aon Shares Held by Shareholders of Record

Aon shareholders of record may vote by proxy or in person at the Aon EGM. Aon recommends that you submit your proxy even if you plan to attend the Aon EGM in person. If you vote by proxy, you may change your vote, among other ways, if you attend and vote at the Aon EGM in person.

If you own shares in your own name, you are considered, with respect to those shares, the “shareholder of record.” If, on the other hand, your shares are held in a stock brokerage account or by a bank or other nominee, you are considered the beneficial owner of shares held in “street name.”

If you are an Aon shareholder of record, you may use the enclosed proxy card to tell the persons named as proxies how to vote your shares. If you are an Aon shareholder of record, the shares listed on your proxy card will include, if applicable, shares held in a book-entry account with Aon’s transfer agent, Computershare Trust Company, N.A.

If you are an Aon shareholder of record and you properly complete, sign and date your proxy card, your shares will be voted in accordance with your instructions. The named proxies will vote all shares at the Aon EGM for which proxies have been properly submitted and not revoked. If you sign and return your proxy card appointing a proxy, but do not mark your card to tell the proxy how to vote on a proposal, your shares will be voted “FOR” such voting proposal.

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If you are an Aon shareholder of record, you may also vote over the internet at www.envisionreports.com/AON2 or by telephone at 1-800-652-8683 anytime up to 11:59 p.m. EDT on August 25, 2020. Voting instructions are printed on the proxy card or voting instruction form you received. Either method of submitting a proxy will enable your shares to be represented and voted at the Aon EGM. You may also hand your applicable completed and signed proxy card to the chair of the Aon EGM before the start of the Aon EGM.

If your shares are held through an Aon employee share plan, you should contact the trustee of your plan for additional information on voting your shares held through an Aon employee share plan.

Voting Aon Shares Held in Street Name

If your Aon Shares are held in an account through a bank, broker or other nominee, you must likewise instruct the bank, broker or other nominee how to vote your shares by following the instructions that the bank, broker or other nominee provides you along with this joint proxy statement. Your bank, broker or other nominee, as applicable, may have different methods by which you are able to provide instructions to it as to how to vote your shares and/or may have an earlier deadline(s) by which you must do so, so you should read carefully the materials provided to you by your bank, broker or other nominee.

If you do not provide a signed voting instruction form to your bank, broker or other nominee, your shares will not be voted on any proposal on which the bank, broker or other nominee does not have discretionary authority to vote. In these cases, the bank, broker or other nominee will not be able to vote your shares on those matters for which specific authorization is required. Brokers do not have discretionary authority to vote on any of the proposals at the Aon EGM.

Accordingly, if you fail to provide a signed voting instruction form to your bank, broker or other nominee, your shares held through such bank, broker or other nominee will not be voted at the Aon EGM.

Revoking your Proxy

If you are an Aon shareholder of record, you may revoke your proxy before it is voted at the Aon EGM by:

Attendance at the Aon EGM will not, in and of itself, revoke a proxy or change your voting instructions; you must vote by ballot at the Aon EGM to change your vote.

If your shares are held in “street name” by a bank, broker or other nominee, you should follow the instructions of your bank, broker or other nominee regarding the revocation of proxies.

Costs of Solicitation

Aon will bear the cost of soliciting proxies from its shareholders in connection with the Aon EGM.

Aon will solicit proxies by mail. In addition, Aon directors, officers and employees may solicit proxies from Aon shareholders by telephone, by electronic communication or in person, but will not receive any additional compensation for their services. Aon will make arrangements with brokerage houses and other custodians, nominees and fiduciaries for forwarding proxy solicitation materials to the beneficial owners of Aon Shares held of record by those persons and will reimburse them for their reasonable out-of-pocket expenses incurred in forwarding such materials.

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Aon has engaged a professional proxy solicitation firm, Georgeson, to assist in soliciting proxies for a fee of approximately $25,000. In addition, Aon will reimburse Georgeson for its reasonable disbursements. Aon also has agreed to indemnify Georgeson against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

Other Business

Aon is not aware of any other business to be acted upon at the Aon EGM. If, however, other matters are properly brought before the Aon EGM, the proxies will have discretion to vote or act on those matters according to their best judgment and they intend to vote the shares as the Aon Board may recommend.

Assistance

If you need assistance in completing your proxy card or have questions regarding the Aon EGM, please contact Aon’s proxy solicitation agent, Georgeson, by mail at 1290 Avenue of the Americas, 9th Floor, New York, NY 10104, by telephone at 1-866-296-5716 or by email at aon@georgeson.com.

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THE TRANSACTION

Structure of the Transaction

On March 9, 2020, Aon and WTW entered into a Business Combination Agreement whereby Aon has agreed to acquire the entire issued share capital of WTW, which acquisition is to be implemented by a way of a court-sanctioned scheme of arrangement to be undertaken by WTW under Chapter 1, Part 9 of the Companies Act. As a result of the scheme, Aon will own all of the outstanding shares of WTW and WTW will become a wholly-owned subsidiary of Aon. The Business Combination Agreement provides that, concurrently with or immediately following April 1, 2020, the effective date of the Aon reorganization pursuant to which Aon Ireland became the public parent company of Aon UK, Aon UK was required to make the required assignment, pursuant to which Aon UK was required to assign, and Aon Ireland was required to assume, all of Aon UK’s rights and obligations under the Business Combination Agreement and the Expenses Reimbursement Agreement. The required assignment occurred on April 2, 2020.

Aon reserves the right, subject to the prior written approval of the Irish Takeover Panel (if required), to effect the transaction by way of a takeover offer, as an alternative to the scheme, in the circumstances described in and subject to the terms of the Business Combination Agreement. In such event, such takeover offer will be implemented on terms and conditions that are at least as favorable to WTW shareholders (except for an acceptance condition set at 80% of the nominal value of the WTW Shares to which such offer relates and which are not already beneficially owned by Aon) as those which would apply in relation to the scheme, among other requirements.

Scheme Consideration to WTW Shareholders

As consideration for the transaction, the holder of each issued and outstanding WTW Share that is subject to the scheme will be entitled to receive 1.08 Aon Shares in exchange for each WTW Share held by such WTW shareholder as more particularly described in the section entitled “The Business Combination Agreement—Scheme Consideration to WTW Shareholders” beginning on page 131 of this joint proxy statement. The implied value of the scheme consideration to WTW shareholders, calculated by multiplying the closing price of an Aon Share on the relevant date by the exchange ratio of 1.08 Aon Shares for each WTW Share, was $184.28 per WTW Share, as of March 4, 2019, the day before the initial market rumors and Aon’s announcement of the parties’ initial exploration of a potential transaction, $231.99 per WTW Share, as of March 6, 2020, the last trading day prior to the announcement of the transaction and $208.01 per WTW Share, as of June 30, 2020, the last practicable trading day before the date of this joint proxy statement. WTW shareholders will not receive any fractional shares of Aon Shares as scheme consideration. Instead, fractional shares will be aggregated and sold in the open market by the exchange agent, with the net proceeds of any such sale distributed in cash pro rata to the WTW shareholders whose fractional entitlements have been sold. Additionally, certain WTW shareholders holding “Consideration Shares” (as defined in the amendment to the articles of association of WTW in the Notice of Extraordinary General Meeting of Willis Towers Watson PLC that accompanies this joint proxy statement) and certain “Overseas Shareholders” (as described in, and subject to, the section entitled “Part 3—The Scheme of Arrangement—The Scheme—Overseas Shareholders” beginning on page 212 of this joint proxy statement) may, depending on certain factors, have a nominee appointed by Aon to act on behalf of and for the benefit of such WTW shareholders, whereby such nominee will, following the effective date, sell such WTW shareholders’ scheme consideration in the open market and deliver the proceeds from such sale to such shareholders (for more information, see the Notice of Extraordinary General Meeting of Willis Towers Watson PLC that accompanies this joint proxy statement and “Part 3—The Scheme of Arrangement” beginning on page 217 of this joint proxy statement). For a description of the treatment of equity awards, see the section entitled “The Business Combination Agreement—Treatment of WTW Equity Awards” beginning on page 131 of this joint proxy statement.

Background of the Transaction

The WTW Board regularly reviews and discusses WTW’s performance, risks, strategy and opportunities, as well as its competitive environment and industry trends. The WTW Board and WTW management also review and evaluate the possibility of pursuing various strategic alternatives and relationships as part of WTW’s ongoing efforts to strengthen its businesses and enhance shareholder value, taking into account economic, regulatory, competitive and other conditions. Similarly, the Aon Board regularly reviews and discusses Aon’s performance,

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risks, strategy and opportunities, as well as its competitive environment and industry trends. The Aon Board and Aon management also review and evaluate the possibility of pursuing various strategic alternatives and relationships as part of Aon’s ongoing efforts to strengthen its businesses and enhance shareholder value, taking into account economic, regulatory, competitive and other conditions.

On November 16, 2018, the Aon Board held a regularly scheduled Aon Board meeting in London, United Kingdom, also attended by members of Aon management. During the meeting, the Aon Board discussed mergers and acquisitions in Aon’s industry and Mr. Case discussed with the Aon Board, at a high level, certain highlights from early analysis of a potential business combination with WTW. Mr. Case expressed interest in reaching out to Mr. Haley and the Aon Board provided its support for Mr. Case doing so. Following the meeting, Aon management contacted Latham & Watkins, LLP, referred to herein as “Latham”, Aon’s outside counsel, to provide Aon with legal advice.

In January 2019, Greg Case, Chief Executive Officer of Aon, and John Haley, Chief Executive Officer of WTW, scheduled a dinner to discuss matters generally affecting the industries in which Aon and WTW operate. Prior to the dinner, Mr. Haley discussed with certain members of WTW management and the WTW Board, including Michael Burwell, Chief Financial Officer of WTW, Brendan O’Neill, a director of WTW and Chair of its Audit Committee and Victor Ganzi, Non-Executive Chairman of the WTW Board, that he had scheduled a dinner with Mr. Case for later that month, and that, since Mr. Haley and Mr. Case did not routinely speak with one another, one potential topic that Mr. Case could raise was a possible business combination between Aon and WTW.

On January 30, 2019, Mr. Case and Mr. Haley met for dinner in Miami, Florida and, in addition to discussing general matters involving the industries in which the companies operate, discussed Mr. Case’s view that Aon and WTW should explore whether a possible business combination of Aon and WTW, potentially structured as a “merger of equals”, would make sense for each company and be feasible. While Mr. Case indicated that Aon likely would expect to provide limited to no premium to WTW shareholders in any such transaction, Mr. Case and Mr. Haley did not engage in negotiations regarding the specific economic terms of any such transaction. Mr. Case and Mr. Haley agreed that they should consider whether a potential transaction between Aon and WTW would provide strategic value to each company’s shareholders and clients, and agreed that it would make sense to have further discussions involving certain senior executives of each company.

On January 31, 2019, Mr. Haley discussed his dinner with Mr. Case with Messrs. O’Neill and Ganzi.

On February 8, 2019, Mr. Case and Mr. Haley had a brief call during which Mr. Case told Mr. Haley that he believed it would be best for Mr. Haley and Mr. Case to have a further discussion before the companies’ respective senior executives met, to ensure everyone’s time was being utilized productively and efficiently. Mr. Haley agreed, and a follow-up meeting was scheduled for March 8, 2019.

On February 15, 2019, the Aon Board held a regularly scheduled Aon Board meeting in Chicago, Illinois, also attended by members of Aon management. During the meeting, Aon management discussed Aon’s business strategy, the strategic rationale for a potential transaction with WTW and potential benefits and risks associated with such transaction. Aon management also discussed, among other things, optimal timing to pursue a transaction and provided the Aon Board with a preliminary regulatory overview. Following the discussion, the Aon Board instructed Mr. Case and Aon management to continue to engage in discussions with WTW management in respect of the potential transaction. Aon management then contacted Aon’s financial advisors to discuss the potential transaction with WTW and engaged Freshfields Bruckhaus Deringer LLP, referred to herein as “Freshfields”, to provide additional legal advice.

On February 27, 2019, the WTW Board held a regularly scheduled WTW Board meeting and, during executive session, Mr. Haley updated the WTW Board on his dinner and follow-up discussion with Mr. Case and the meeting with Mr. Case that was scheduled for March 8, 2019.

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On March 5, 2019, news outlets reported speculation about a potential transaction between WTW and Aon. WTW management contacted WTW’s legal advisors Matheson and Weil, Gotshal & Manges LLP, referred to herein as “Weil”, to discuss the market rumors and WTW’s obligations with respect to such rumors. Throughout the course of the day, Messrs. Case and Haley, in addition to certain other members of management of each company, discussed various matters, including the content of any public statements required under Irish law to be made regarding the high-level discussions that had taken place. Later that day, pursuant to the Irish Takeover Rules, Aon publicly announced that it was in the early stages of considering an all-share business combination with WTW.

Later that day, the WTW Board scheduled a telephonic informational update, to be held early the next morning, to discuss the market rumors, as well as Aon’s March 5th public statement, and to consider potential next steps.

Early in the morning on March 6, 2019, Aon issued a press release announcing that it did not intend to pursue a transaction with WTW, and, as a result of such announcement, Aon became bound by the restrictions set forth in Rule 2.8 of the Irish Takeover Rules, which precluded, for a period of 12 months, among other things, an announcement by Aon of a proposal for a transaction with WTW subject to certain exceptions. Prior to the issuance of the press release, Mr. Case informed the Aon Board via email that all plans concerning a possible transaction with WTW had been discontinued.

Later that morning, the WTW Board held a telephonic informational update and discussed Aon’s March 5th public statement and March 6th press release and considered WTW’s obligations and potential next steps. Following discussion, the WTW Board agreed that no further action or statement by WTW was necessary, given Aon’s public statement, and the WTW Board’s view was that, after considering all the relevant facts and circumstances, no further discussion with Aon was warranted at that time.

On March 29, 2019, the Aon Board held a regularly scheduled Aon Board meeting in London, United Kingdom, also attended by members of Aon management. During the meeting, Mr. Case led a discussion regarding the market rumors, the discussions between himself and Mr. Haley and the press releases issued by Aon on March 5 and 6, 2019, and reminded the Aon Board that all plans concerning a possible transaction with WTW had been discontinued and that Aon’s internal and external teams had been instructed to cease all efforts in pursuit of a potential transaction with WTW.

On May 12, 2019, Mr. Case called Mr. Haley and, among other matters discussed on the call, including general industry developments, Mr. Case indicated that within the parameters of Rule 2.8 of the Irish Takeover Rules, Aon and WTW could consider discussing the merits of a combination of the two companies because such a discussion had been preempted by news outlets reporting speculation about a potential transaction in March. Such discussion would inform any decision by WTW whether to initiate negotiations of a potential transaction between the two companies.

On May 14, 2019, Mr. Haley called Mr. Case and informed Mr. Case that Mr. Haley would consult with the WTW Board regarding Mr. Case’s suggestion that they discuss the merits of a combination of the two companies.

On May 20, 2019 and May 21, 2019, at regularly scheduled WTW Board meetings in Dublin, Ireland, Mr. Haley discussed with the WTW Board the call with Mr. Case, as well as the possibility of discussions of a potential combination. Following discussion, the WTW Board determined that Mr. Haley should proceed with initial, high-level discussions with Mr. Case and report back to the WTW Board. During the WTW Board meetings, Mr. Haley also discussed with the WTW Board the possibility of engaging Goldman Sachs to assist WTW and the WTW Board with respect to strategic matters, including if WTW were approached by any potential strategic acquiror, or faced any shareholder activism given the news stories and announcements with respect to a combination with Aon and general market conditions. After discussion of the relevant facts and

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