OMNICOM GROUP INC.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

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:

☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☑ Definitive Proxy Statement

☐ Definitive Additional Materials

☐ Soliciting Material under §240.14a-12

Omnicom Group Inc.

(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 ALL BOXES THAT APPLY):

☑ No fee required

☐ Fee paid previously with preliminary materials

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

A Letter from Omnicom’s Lead Independent Director

To My Fellow Shareholders:

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.

Mary C. Choksi

Lead Independent Director

2 2026 Proxy Statement

NOTICE OF 2026 ANNUAL MEETING OF

SHAREHOLDERS

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

ITEM 1: Election of Directors

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.

See page 13for furtherinformation

DIRECTOR NOMINEES

4 2026 Proxy Statement

Board Nominees Snapshot

Experience, Skills and Composition

Our director nominees are accomplished leaders who bring a mix of experiences and skills to the Board.

Our Board has identified skill categories fundamental to its ability to effectively oversee Omnicom’s current and forward-looking strategy and management, and undertakes a comprehensive evaluation so that these skills are well represented on the Board.

Three former directors of The Interpublic Group of Companies, Inc. (“IPG”), including IPG’s former Chief Executive Officer, Philippe Krakowsky, joined the Board on November 26, 2025 (the “Closing Date”), upon the closing of our acquisition of IPG. The directors bring fresh perspectives, a strong mix of valuable skills, and a deep understanding of IPG’s companies to the Board. The addition of these directors strengthens our Board’s ability to effectively oversee the combined company integration and management’s execution against business strategy.

Prior to the former IPG directors joining the Board, Cassandra Santos joined the Board on January 1, 2024 as part of our continued refreshment process. Ms. Santos contributes relevant technology, cybersecurity, digital transformation and AI expertise to the Board.

Our Board is comprised of seven women and seven men. Four of our directors are Black, two are Hispanic and eight are White.

See pages 14 and 15 for further information.

6 2026 Proxy Statement

GOVERNANCE HIGHLIGHTS

The Board has adopted, and periodically reviews, policies and procedures to guide it in its oversight responsibilities. These policies and procedures provide a framework for the proper operation of our Company and align with shareholders’ interests.

SHAREHOLDER ENGAGEMENT

Ongoing shareholder engagement is a priority for our Board and management team. In the fall of 2025, we reached out to shareholders holding 75% of our outstanding shares with an invitation to engage. We spoke to every shareholder that accepted our invitation, which represented an aggregate of 30% of our outstanding shares. As in prior years, our Lead Independent Director was an active participant in select shareholder meetings. Broad topics discussed included:

■Company strategy and performance

■Board composition, refreshment and leadership

■IPG acquisition and integration

■Management succession planning

■Executive compensation program

■Governance practices

■Human capital management initiatives

We have made a number of changes in recent years that are aligned with perspectives shared through ongoing shareholder engagement efforts, which management regularly reviews with the Board, including:

8 2026 Proxy Statement

We appreciate the insights and perspectives of our shareholders, which were discussed among the full Board.

ITEM 2: Advisory Resolution to Approve Executive Compensation

The Board recommends a vote FOR this voting item. ■ We closely tie pay to current and long-term Company performance. ■ We maintain a high degree of variable “at-risk” compensation. ■ With a focus on the successful integration of IPG, the continued transformation of Omnicom’s business in a new era of marketing and sales, and forward-looking succession planning, the Board (upon recommendation of the Compensation Committee) granted Mr. Wren a special award of stock options, and Mr. Wren agreed to reduce his annual base salary to $1 and forgo any other incentive compensation through the end of fiscal year 2028. These changes are intended to drive long-term shareholder value creation. ■ For our other eligible NEOs, we (i) established challenging quantitative performance metrics that align with our business strategy and support alignment between Company performance and pay outcomes, which determined 50% of our 2025 Annual Incentive Award, and (ii) determined the other 50% of our 2025 Annual Incentive Award by assessing certain qualitative performance metrics tied to the successful closing of the IPG transaction, the integration of IPG and individual performance. ■ We sustain competitive compensation levels.

See page 42for furtherinformation

EXECUTIVE COMPENSATION HIGHLIGHTS

CHAIRMAN AND CEO COMPENSATION REDESIGN

The Compensation Committee recognized the strategic importance of securing Mr. Wren’s continued leadership through this period of unprecedented transformational change, integration and opportunity and entered into an amended and restated employment agreement with Mr. Wren, pursuant to which he agreed to extend his employment as Omnicom’s Chairman and Chief Executive Officer through December 31, 2028, at which point he would continue as Executive Chairman of the Board. During this time, the Lead Independent Director and Board will work with Mr. Wren to identify his successor as CEO to ensure a smooth succession process. In connection with his amended and restated employment agreement, the Board (upon recommendation of the Compensation Committee) granted Mr. Wren a special award of stock options, and Mr. Wren agreed to reduce his annual base salary to $1 and forgo any other cash or equity incentive compensation through the end of fiscal year 2028. These changes are intended to drive long-term shareholder value creation and, as a result, his incentive compensation will be completely at-risk and dependent on Omnicom’s future stock price.

OTHER NEO ANNUAL INCENTIVE AWARD DESIGN

The chart below outlines the metrics used in determining our Annual Incentive Award for 2025 for our NEOs, other than our Chairman and CEO. The program is discussed in greater detail below in the section entitled “Calculation of Annual Incentive Award” on page 56.

10 2026 Proxy Statement

Compensation Best Practices

Emphasis on performance-based compensation Executive and director stock ownership guidelines (6x base salary for Chairman and CEO and for Co-Presidents and Co-COOs; 3x base salary for CFO; 5x annual cash retainer for directors) Policy adopting equity grant best practices Compensation recovery (i.e., clawback) policy in compliance with U.S. Securities and Exchange Commission (“SEC”) and New York Stock Exchange (“NYSE”) rules Policy prohibiting hedging of Company equity securities Policy prohibiting pledging and margin transactions

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

The Board recommends a vote FOR this voting item.

See page 77for furtherinformation