The world's second-largest agency holding company planned to formally release the information after close of market today.
The new Omnicom board will consist of 11 members, nine from outside the company.
"This is something that's been talked about for the last several years," Mr. Wren said. "There's a very strong feeling that boards should be between nine and 12 members, and it should be clearly dominated by non-employee directors."
Stepping down after the May 21 shareholder meeting will be Bernard Brochand, former vice chairman, DDB Worldwide; James A. Cannon, vice chairman and chief financial officer, BBDO Worldwide; Jean-Marie Dru, president-CEO, TBWA Worldwide; Michael Greenlees, executive vice president, Omnicom Group; Thomas L. Harrison, chairman-CEO, Diversified Agency Services; Keith Reinhard, chairman, DDB Worldwide; and Allen Rosenshine, chairman-CEO, BBDO Worldwide.