GroupM has appointed Kelly Clark as global chief executive, replacing Dominic Proctor.
Dominic, who has run GroupM globally since 2012, will continue to work for GroupM on strategic projects.
Irwin Gotlieb, global chairman of GroupM, said: "Dominic helped make Mindshare and GroupM the successful global businesses they are today. It has been a great pleasure to work side by side with Dominic over many years and we all wish him the very best.
Most recently Clark was working on consultancy projects for GroupM. He stepped down from his role as chief executive of GroupM in North America in November last year after deciding he wanted a less time-consuming role.
Prior to becoming North America chief executive in 2012, Clark was the global chief executive of Maxus from 2008.
Gotlieb said: "Kelly has demonstrated inspiring leadership at every turn in his career, and he has earned the respect of our clients and our people.
"He has broad experience in North America, Asia and Europe and is focused intensely on delivering advantage to our clients. I am looking forward to working with him to build on our momentum."