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

(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

PROXY STATEMENT

Annual Meeting of Shareholders

May 6, 2025, at 10:00 a.m.

Eastern Daylight Time

www.virtualshareholdermeeting.com/OMC2025

A Letter from Omnicom’s Lead Independent Director

To My Fellow Shareholders:

I am grateful to be writing to you on behalf of the Board of Directors as I reflect on my first full year as Lead Independent Director. The past year was bookended by milestone events for our Company, emblematic of our leadership team’s relentless pursuit of strategic opportunities for growth, while building on Omnicom’s legacy of providing exceptional work to our clients. In January 2024, we closed on the acquisition of Flywheel, which represented Omnicom’s largest acquisition to date, followed by our acquisition of LeapPoint in September 2024, both of which bolstered our efforts to leverage world-class technology capabilities and artificial intelligence (AI) to improve client and customer experiences. Most significantly, we ended the year by announcing our agreement to acquire Interpublic Group (IPG) in December, which we expect to complete in the second half of 2025, and which will create the industry’s deepest and broadest bench of talent and services driven by an unmatched sales and marketing platform. I am extremely optimistic for what is ahead for Omnicom and its shareholders.

These strategic actions exemplify Omnicom’s commitment to serving our clients and creating value for shareholders by attracting and retaining top tier talent, growing digital and e-commerce offerings, accelerating innovation, and improving outcomes. Omnicom’s work and success have always been underpinned by our ability to evolve our capabilities to meet client needs in a complex marketing and technology landscape. My fellow Board members and I have been keenly focused on ensuring that we are prepared for the impact generative AI will have on our business, and Omnicom is taking a responsible and strategic approach to its use and integration. We have formed industry-leading strategic partnerships and implemented technologies across our business with the goal of empowering our people and facilitating development and deployment of creative solutions, extending our capabilities and driving growth opportunities.

Under the strategic direction of our Chairman and CEO, John Wren, our Board has overseen management’s deployment of a number of successful initiatives that have transformed our business for long-term success in a rapidly evolving industry. We are particularly excited for the opportunities that our pending acquisition of IPG will bring. Looking forward, I am certain that we have the right Board to serve Omnicom and its shareholders through this pivotal moment in our strategic journey. Through our purposeful refreshment efforts and an effective Board leadership structure, we have the skills, experience, and independence in place to successfully oversee this next stage in Omnicom’s evolution. We look forward to welcoming the entire IPG team, including CEO Philippe Krakowsky, who will serve as Omnicom’s Co-President and Co-Chief Operating Officer and director, and whose demonstrated strategic leadership and extensive industry knowledge will strengthen our Board and management team.

During this past year, I greatly appreciated the opportunity to engage in constructive dialogue with shareholders in my new role as Lead Independent Director, which included discussions around governance and Board leadership practices. Shareholders provided valuable perspectives, including support for our Board leadership structure and recognition of the importance of maintaining a flexible approach during this critical period of our Company’s evolution. I look forward to the coming year as we shift our focus to planning the integration of IPG and taking advantage of new strategic opportunities.

We invite you to read more about our activities in 2024 and key areas of focus for the Board in this year’s proxy statement. On behalf of the full Board, I thank you for your investment in Omnicom and consideration of these important matters.

Mary C. Choksi

Lead Independent Director

2 2025 Proxy Statement

NOTICE OF 2025 ANNUAL MEETING OF

SHAREHOLDERS

This summary highlights selected information about the items to be voted on at the 2025 Annual Meeting of Shareholders (or “2025 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. ■ 10 of Omnicom’s 11 director nominees are independent, and each of the Audit, Compensation, Governance and Finance Committees is comprised solely of independent directors.

See page 12for furtherinformation

DIRECTOR NOMINEES

4 2025 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.

One new director joined the Board on January 1, 2024 as part of our continued refreshment process to bring fresh perspectives to the Board. This director brings relevant technology, cybersecurity, digital transformation and AI expertise, which strengthens our Board’s ability to effectively oversee management’s execution against business strategy.

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

See pages 13 and 14 for further information.

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 2024, we reached out to shareholders holding 70% of our outstanding shares with an invitation to engage. We spoke to every shareholder that accepted our invitation, which represented an aggregate of 26% 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

■Management succession planning

■Executive compensation program

■Governance practices

■Human capital management initiatives

■Environmental initiatives

6 2025 Proxy Statement

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:

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; ■ We establish challenging quantitative performance metrics that align with our business strategy, which determined 80% of our 2024 Annual Incentive Award; ■ We determined 20% of our 2024 Annual Incentive Award by assessing certain qualitative performance metrics to increase alignment between executive and Company performance and pay outcomes; and ■ We sustain competitive compensation levels.

See page 38for furtherinformation

8 2025 Proxy Statement

EXECUTIVE COMPENSATION HIGHLIGHTS

2024 Performance Overview and Highlights

Omnicom finished 2024 on a strong note. Our full year revenue was $15,689.1 million, with organic growth of 5.2%; operating income for 2024 compared to 2023 increased $169.9 million, or 8.1%, to $2,274.6 million, and operating margin increased to 14.5% from 14.3% due to factors discussed in our Annual Report on Form 10-K for the year ended December 31, 2024 (the “2024 10-K”). Net income – Omnicom Group Inc. increased by $89.2 million to $1,480.6 million, EBITA increased $195.6 million to $2,362.1 million, EBITA margin increased to 15.1% from 14.7% and diluted Earnings per Share increased to $7.46. We generated approximately $1.7 billion in net cash provided by operating activities, an increase of 21.9% compared to the full year 2023, and approximately $2.0 billion in free cash flow, an increase of 4.2% compared to the full year 2023. We returned over $900 million to shareholders through dividends and share repurchases and ended the year with $4.3 billion in cash and cash equivalents. See Annex A for the definitions of adjusted operating income, adjusted operating margin, EBITA, EBITA margin and free cash flow, which are non-GAAP measures, and a reconciliation of each non-GAAP measure to the most directly comparable GAAP measure. Our return on equity was 37.9% in 2024, while our return on invested capital was 24.9%.

On December 9, 2024, Omnicom and The Interpublic Group of Companies, or IPG, announced that they had entered into a merger agreement pursuant to which Omnicom will acquire IPG in a stock-for-stock transaction, or the Merger. Additional information regarding the transaction can be found in the Compensation Discussion and Analysis on page 46 below. We believe the combined company will bring together the industry’s deepest bench of marketing talent and the broadest and most innovative services and products, driven by the most advanced sales and marketing platform. Together, the companies are expected to expand their capacity to create comprehensive solutions that deliver better outcomes for clients.

Completion of the Merger is subject to customary closing conditions, including required regulatory approvals. The stockholders of each company overwhelmingly approved the acquisition at their respective Special Meetings of Stockholders held on March 18, 2025. The Merger is expected to close in the second half of 2025. If completed, the Merger is expected to have a material impact on our ongoing results of operations and financial condition. In the fourth quarter of 2024, we recorded $14.6 million of acquisition transaction costs related to the Merger in selling, general and administrative expenses. The results of IPG are not included in our 2024 results of operations or financial position.

In determining the Annual Incentive Award for performance in 2024, the Compensation Committee considered Company (i.e., internal) financial performance (weighted at 40%), our performance as compared with the performance of our peer group (weighted at 40%) and certain qualitative metrics (weighted at 20%) to increase alignment between executive and Company performance and pay outcomes and further strengthen pay and performance alignment.

The chart below outlines the metrics used in determining our Annual Incentive Award for 2024. The program is discussed in greater detail below in the section entitled “Calculation of Annual Incentive Award” on page 51.

Compensation Best Practices

Emphasis on performance-based compensation Executive and director stock ownership guidelines (6x base salary for Chairman and CEO and for President and COO; 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, 2025

The Board recommends a vote FOR this voting item.

See page 70for furtherinformation

ITEM 4: Shareholder Proposal Regarding an Independent Board Chairman

The Board recommends a vote AGAINST this voting item.

See page 72for furtherinformation

10 2025 Proxy Statement