The merger of the two companies was agreed at the end of 2024, with Omnicom shareholders owning 60.6% of the combined company and Interpublic shareholders own 39.4%, on a fully diluted basis.

Earlier this week, the European Commission granted antitrust approval to the acquisition, which was the last regulatory clearance needed to complete the transaction. The Competition and Markets Authority granted approval in the summer.

The combined company has combined revenue of greater than $25bn, and it will trade under the OMC ticker symbol on the New York Stock Exchange.   

Omnicom is the owner of networks Omnicom Media Group (OMG), Flywheel and the DAS Group of Companies. Businesses include advertising group DDB, data and analytics division Annalect, branding agency Interbrand and media agency Hearts and Science.

Interpublic’s agencies include media network UM, advertising agencies FCB and McCann and media and marketing services arm IPG Mediabrands.

John Wren will remain in place as chairman and chief executive, Phil Angelastro is executive vice-president and chief finance officer, and Philippe Krakowsky and Daryl Simm still serve as co-presidents and chief operating officers.

Philippe Krakowsky, Patrick Moore and E Lee Wyatt Jr have also joined the Omnicom board of directors. The company’s full leadership team will be announced on 1st December.  

Wren said: “This is a defining moment for our company and our industry.

“We’re excited about this next chapter. I want to thank our people, clients and shareholders for the trust they have placed in us.”