Laura Desmond, chief executive of Starcom MediaVest Group in the Americas, will take over McCann's role, effective immediately.
McCann will now spend the next six months working on talent-related group-level projects and continue to report to Jack Klues, chairman of Publicis Groupe Media. She will also help Desmond in her transition into the global chief executive role.
Klues said: "It is impossible to summarise the contributions Renetta continues to make to our business and to the industry at large.
"She has earned the opportunity to step back from the global role and reassess the contributions she wants to make moving forward."
McCann said in a statement: "I have been given the opportunity to build an incredible organisation during a decade of management responsibility, but I now recognise that some family matters and personal goals have unfortunately taken a back seat during this time. I would like to give them my full attention now."
McCann assumed the role of global chief executive at Starcom MediaVest Group in 2005. Before that, she was chief executive of Starcom MediaVest Group in the Americas.
Desmond said: "I was not expecting to fill the global CEO role at this point in my career.
"But the fact that I am prepared to do it is a testament to Renetta McCann, to the remarkable talent that populates this network, and to the forward-thinking clients that have challenged and inspired me to constantly up my game. I have tremendously large shoes to fill without a doubt, but I also have powerful momentum to build on."
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