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. )

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Check the appropriate box:

☐ Preliminary Proxy Statement

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☑ 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)

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PROXY STATEMENT

Special Meeting of Shareholders

January 28, 2026, at 10:00 a.m.

Eastern Standard Time

www.virtualshareholdermeeting.com/OMC2026SM

NOTICE OF SPECIAL MEETING OF

SHAREHOLDERS

2 2026 Proxy Statement

PROXY STATEMENT

Dear Shareholders,

On behalf of the Board of Directors (the “Board”) of Omnicom Group Inc. (the “Company,” “Omnicom,” “we,” “us” or “our”) we are pleased to invite Omnicom shareholders as of the close of business on December 17, 2025, the record date, to virtually attend a special meeting on Wednesday, January 28, 2026, at 10:00 a.m. Eastern Standard Time (the “Special Meeting”), via live webcast at www.virtualshareholdermeeting.com/OMC2026SM.

At the Special Meeting, Omnicom shareholders will be asked to vote on a proposal to approve the Omnicom 2026 Incentive Award Plan (the “Plan”). In preparing for the acquisition of The Interpublic Group of Companies, Inc. (“IPG”), which closed on November 26, 2025, the Board carefully evaluated the equity needs of the combined company. We determined that adopting the new Plan, including an expanded share reserve relative to our existing equity program, is both necessary and appropriate to maintain sufficient shares to support retention and incentivization of our enlarged workforce for the combined go-forward company. The Plan also supports the broader objectives of our compensation program, equity usage and talent strategy by aligning the incentives of Omnicom’s employees, directors and consultants with those of our shareholders and with company performance.

Your vote is very important. To ensure your representation at the Special Meeting, please complete and return the applicable enclosed proxy card or submit your proxy by phone or the Internet. Please vote promptly, whether or not you expect to virtually attend the Special Meeting. Submitting a proxy now will not prevent you from being able to vote at the Special Meeting.

Sincerely, Mary C. ChoksiLead Independent Director

The proxy statement is dated December 22, 2025 and is being made available to the holders of record and beneficial owners of shares of our common stock as of the close of business on the December 17, 2025 record date. Omnicom’s address is 280 Park Avenue, New York, New York 10017.