EXHIBIT 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

Omnicom Group Retirement Savings Plan

New York, New York

We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (No. 333-74591) of Omnicom Group Inc. of our report dated June 25, 2021 relating to the financial statements and supplemental schedules of the Omnicom Group Retirement Savings Plan, which appears in this Annual Report on Form 11-K.

/s/ PKF O'Connor Davies LLP

Harrison, New York

June 25, 2021

15