Chris Pearce, chief executive of TMW Unlimited, is set to leave the agency.
His next steps are not yet known, but he will remain in advertising.
Alex Burley will take over Pearce's role in the interim and has been promoted to the newly created position of chief operating officer. TMW said Burley will be supported by founding partner Richard Marshall.
Pearce has been at TMW for more than 11 years, having joined as business director. He was appointed chief executive in 2015.
During Pearce's tenure, TMW was awarded Campaign’s Customer Agency of the Year in 2016.
The CRM agency works with clients including Morrisons, Coty, Nissan Europe and Shell Retail.
Tim Bonnet, president of Unlimited Group, said: "Chris has made a great contribution to TMW over the last 11 years. We thank him for all his hard work and wish him the very best for the future."