Omnicom Group Inc.

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A Letter from Omnicom's Lead Independent Director

This past year was one of significant transformation for Omnicom, capped by our successful acquisition of The Interpublic Group of Companies (IPG), creating the world's leading marketing and sales company, built for intelligent growth in the next era. Together with the acquired IPG companies, the new Omnicom unites the industry's most comprehensive and connected portfolio of capabilities, creating stronger brands, delivering superior business outcomes, and driving sustainable growth. We are actively leveraging strategic advantages resulting from the IPG acquisition, which provide a competitive edge across every dimension of state -of-the-art marketing and sales, including our media ecosystem, influential content, connected commerce excellence, enterprise generative AI capabilities, and identity solutions. Built on these combined strengths, in January we launched the new Omni, our next generation marketing intelligence platform, which uses leading -edge AI to capture the full breadth of the marketing ecosystem and empower our client leaders in doing their most creative and intelligent work. We also recently hosted an Investor Day, where we shared an update on Omnicom's go -forward strategic priorities and capital allocation strategy, including the $5 billion dollar share repurchase program approved by the Board earlier this year.

Throughout our planning for the IPG acquisition, the Board remained focused on identifying our industry's most exceptional talent and building a dedicated, expert leadership team to guide execution of our strategic objectives and deliver long -term shareholder value, appointing several leaders across our connected capabilities and enterprise -wide teams by the close of 2025. Our Chairman and CEO, John Wren, has provided clear and consistent leadership during this pivotal time, building on Omnicom's competitive advantages, retaining top talent, and navigating relationships with clients. His continued leadership in the coming years, as clarified in his amended employment agreement, will provide critical continuity and execution of our strategy through this period of integration and transformation. As we look ahead, the Board remains focused on CEO and senior management succession planning, as well as talent development for our senior leadership team to ensure a smooth transition at the appropriate time.

The Board was pleased to welcome three new directors from IPG's board in November: former IPG CEO Philippe Krakowsky, who also assumed the role of Omnicom's Co -President and Co -COO , and independent directors Patrick Moore and Lee Wyatt, who bring deep industry knowledge, financial expertise, and experience across technology and digital transformation to the boardroom. Their addition to the Board enhances the overall mix of perspectives and relevant skill sets our directors collectively possess, supporting effective oversight of Omnicom's business.

We are well positioned for future growth as our Chairman and CEO, John Wren, along with the Company's management team, and our exceptionally talented global workforce drive our business forward, setting the standard for marketing and sales leadership by providing unmatched services to the world's leading brands and innovative solutions to their most critical growth challenges. My fellow directors and I look forward to working with management as we move forward in this new era for Omnicom. On behalf of the Board, thank you for your continued support and investment in Omnicom.

NOTICE OF 2026 ANNUAL MEETING OF SHAREHOLDERS

1. Elect the director nominees named in the Proxy Statement accompanying this notice to Omnicom Group Inc.'s (the "Company," "we," "us"or"our") Board of Directors (the "Board") to serve until the Company's 2027 Annual Meeting of Shareholders or until the election and qualification of their respective successors.

2. Vote on an advisory resolution to approve executive compensation.

3. Ratify the appointment of KPMG LLP as our independent auditors for the fiscal year ending December 31, 2026.

The Board unanimously recommends that you vote:

■ FOR the advisory resolution to approve executive compensation; and

■ FOR the ratification of the appointment of KPMG LLP as our independent auditors.

The 2026 Annual Meeting of Shareholders will be held in a virtual meeting format only, via live webcast, and there will not be a physical meeting location. You will be able to attend the 2026 Annual Meeting of Shareholders online and vote your shares and submit questions electronically at the meeting. Shareholders will also transact any other business that is properly presented at the meeting. At this time, we know of no other matters that will be presented.

Please sign and return your proxy card or vote by telephone or Internet (instructions are on your proxy card or Notice of Internet Availability of Proxy Materials), so that your shares will be represented at the 2026 Annual Meeting of Shareholders, whether or not you plan to attend. You may attend the 2026 Annual Meeting of Shareholders online by visiting www.virtualshareholdermeeting.com/OMC2026 and entering the 16 -digit control number included on your Notice of Internet Availability of Proxy Materials or proxy card. Additional information about the meeting is included below in the Proxy Statement in the section entitled "Information About Voting and the Meeting."

www.virtualshareholdermeeting.com/OMC2026

This summary highlights selected information about the items to be voted on at the 2026 Annual Meeting of Shareholders (or "2026 Annual Meeting"). This summary does not contain all of the information that you should consider in deciding how to vote. You should read the entire Proxy Statement carefully before voting.

Meeting Agenda and Voting Recommendations

The Board recommends a vote FOR each of the director nominees.

■ We have conducted a comprehensive evaluation of director skill sets to enable each director's unique qualifications and attributes to collectively support the oversight of Omnicom's management.

■ Each of our directors is elected annually by a majority of votes cast.

■ 12 of Omnicom's 14 director nominees are independent, and each of the Audit, Compensation, Governance and Finance Committees is comprised solely of independent directors.

Mary C. Choksi, ( I ), 75 Lead Independent Director

Former Founding Partner and Senior Managing Director, Strategic Investment Group

Former President, National League of Professional Baseball Clubs

Former Vice Chair and Regional Managing Partner, EY

Co-President and Co-Chief Operating Officer, Omnicom

Former President and Chief Executive Officer, TEGNA Inc.

Chief Executive Officer, Opry Entertainment Group

Former Group Vice President of Hispanic Business Strategy, Toyota Motor North America

Chief Executive Officer, Johnson Publishing Company

Chairman and Chief Executive Officer, Omnicom

Former Senior Vice President and Chief Financial Officer, Fortune Brands