Kelly Clark is to step down as global chief executive of Group M, the world’s biggest media buyer, and Christian Juhl, the global chief executive of one of its flagship agencies, Essence, will take over.
It is thought that Clark wants to step back for personal reasons after three years in charge.
It is the second time he has relinquished the role after taking a break in 2015, before returning in 2016.
Juhl, who is American, has a reputation as a digital-savvy leader who took over the leadership of Essence from its three, British co-founders and sold it to WPP in 2015.
Essence is best known as Google’s agency and it was apparent that Juhl’s star was on the rise when he was invited to speak at new WPP chief executive Mark Read’s investor day in London in December.
Read said: "Christian has the right combination of leadership, people and technology skills to build the modern media company, something he has demonstrated extraordinarily well at Essence.
"We have a great number of talented people across Group M and its agencies, and I have every confidence in Christian’s ability to be an outstanding leader to them and an outstanding partner to our clients."
It is understood that WPP did not carry out a full search for Clark’s replacement but was keen to make a "forward-looking" appointment of a leader who could hold the job for five to ten years.
Juhl, who previously held roles with Publicis Groupe and Razorfish, said: "I’m truly honoured and grateful for this opportunity to help deliver on Mark’s vision for WPP as a creative transformation company.
"Media frames the future for creativity, and Group M's incredible agency brands, talent, client partnerships, and scale give us the unique opportunity to help reshape the industry and the way people think about advertising."
Clark’s main period in charge of Group M from 2016 to 2019 has been turbulent as a generation of older leaders, including Irwin Gotlieb, the global chairman, and Rob Norman, the chief digital officer, stepped down.
He took the helm soon after Group M suffered two heavy blows when it lost Volkswagen Group and AT&T in 2016 and just months after the Association of National Advertisers published a report in media buying transparency in the United States.
Group M, like its parent company, WPP, went on to suffer other client losses including American Express and GlaxoSmithKline and it merged two agencies, MEC and Maxus, to form Wavemaker.
But it also showed signs of recovery under Clark’s leadership, winning Adidas and expanding its brief with Mars last year.
More recently, the WPP buying arm had further success this year, using Essence to retain L’Oreal, which was previously held by sister agency Wavemaker, and helping to win Centrica’s global integrated pitch.
Clark will continue as a senior adviser to WPP and Group M.
He said: "Today, we’re stronger and better-positioned to help our clients win in an intensely competitive business environment.
"I know Christian will work well with our leadership team to build further and faster on our ability to contribute to client growth. All of us in Group M have an inspiring new leader."
Read said: "Kelly has had a very successful three years as CEO of Group M, reflected in its recent strong run of new business wins.
"I’d like to thank him for his dedication and leadership over many years with the company. I am delighted that he will support Christian during the transition and continue as a trusted senior advisor to the company."