In her new role, Ms. Desmond, 41, will supervise all of the group's U.S., Canadian and Latin American units, including mainline media agencies MediaVest and Starcom, and the more specialized shops GM Planworks, Halogen and Tapestry.
The position was last filled by current Starcom MediaVest Group CEO Renetta McCann, who left the post for the top job late last year.
"Digital won't be an option, it will be a mindset," Ms. Desmond said in a statement. "We will drive the capabilities across the entire employee population. My key priorities for the near term are going to be in response to the dynamic industry we are facing: digital expertise, talent development and one-to-one marketing."
A spokeswoman said Ms. Desmond will continue to serve as CEO of MediaVest for now, but that she'll likely be shifting many of those responsibilities over to other members of the agency's leadership team soon.
Nineteen years with Publicis
Ms. Desmond joined Publicis' media empire in 1987 as an associate at what was then called Leo Burnett Media, and during her subsequent ascent she worked on and supervised major accounts such as Heinz, McDonald's, Kellogg, Coca-Cola and General Motors.
She was named CEO of the group's Latin American unit in 2000, and two years later was named CEO of MediaVest.