Jon Peppiatt, chairman of Bartle Bogle Hegarty, has been made redundant after 25 years at the agency.
The exit is part of the agency's leadership team move to reshape the business.
Peppiatt took on the chairman role in 2015 following the departure of Jim Carroll and has been leading the agency’s new-business efforts, winning accounts such as Ladbrokes Coral Group.
He was previously deputy chairman, having been promoted from resource director in 2007 under previous chief executive Ben Fennell.
Along with Fennell, Carroll, ex-managing director Charlie Rudd and former executive creative director Nick Gill, Peppiatt was a long-standing member of the management team and in 2012 helped steer BBH to win Campaign’s Agency of the Year accolade.
Peppiatt, who is best known by the moniker "Pep", started his career in the post room at CDP before working his way up to the top of one of the UK’s most famous agencies.
Neil Munn, group chief executive of BBH, said: "Pep is a brilliant and unique figure in our industry. A figure who spans the generations. He is the person that you want by your side on a challenging mission. Generous, resourceful, thoughtful and wise. We have been privileged to have Pep with us for the last 25 years and are immensely grateful for all that he has given to BBH."
Peppiatt will leave towards the end of the year. He said: "I've loved my time at BBH and it's been an absolute pleasure and a privilege working at such a wonderful company for so long. I have learnt from the very best and have got to work with an unbelievable amount of brilliant people over the years. There have been so many highs and I feel very lucky to have been part of it all. But I'm off towards the end of the year. I am sad, of course, but also excited about what's next. Onwards and Upwards."
In April, parent company Publicis Groupe UK announced plans to cut some of its 5,000 jobs because of the impact that coronavirus has had on business.