The proposed merger will create the largest family of ad agencies in the world and have a stock market value of $35.1 billion, The New York Times reported.
Once approved by U.S. and French regulators, the new company will include major firms such as Leo Burnett, and Saatchi-and-Saatchi. Its client portfolio included McDonald's, Wal-Mart, Coca-Cola and Pepsi.
Omnicon Chief Executive Officer John Wren and Publicis Chairman and CEO Maurice Levy will serve as co-chief executives for at least the near term.
A key to the merger plan is the current evolution of so-called big data, the Times said.
The introduction of massive flows of information about consumers has blurred the historic lines in the ad industry and required firms to provide a wider range of digital services.
"Omnicom and Publicis Groupe are reshaping the industry by setting a new standard for supporting clients with integrated messaging across marketing disciplines and geographies," Wren said in a written statement.