Peter Zillig is stepping down as chief executive of Cheil UK after more than three years.
David Coombs, head of strategic services, will take over from 1 July.
Zillig handed in his notice in February and will stay at Cheil until the end of June in an advisory position. He plans to "take up a new client-side opportunity" that has yet to be announced.
Joining in 2016, Zillig has helped Cheil more than double its revenue by developing new products and services to build a business that has more than 60% of its income from digital marketing.
Coombs has worked at Cheil for four years, reporting to Zillig. He has previously worked as head of planning at AKQA and digital strategy director at OMD.
The UK shop has almost 200 employees.
Byunghoon So, Cheil’s European chief executive and president, said: "It’s been a pleasure working alongside Pete, who has created significant growth and change in the business during his tenure.
"Dave’s digital heritage and strategic mind makes him the ideal candidate and obvious choice to continue this growth story for Cheil UK. I look forward to working with Dave and the rest of the management team to drive our performance marketing capability and our full-service offering."