Supple is looking for a new role in an independent agency, but does not have a role lined up yet.
Supple joined Carmichael Lynch as a copywriter in 1979. Since then, he has been the agency's executive creative director and president before being promoted to chairman and chief creative officer in 2000.
"I've been through all the roles here. This last one is not satisfying," Supple said in a statement. "I feel under-utilised. Being the chairman is like being Chuck E Cheese: you're like a fun character, but you're not as involved as you'd like to be."