He will leave as managing partner of the £45 million-billing shop on his 50th birthday next April to begin a new career as a motivational business speaker and trainer.
Hesketh will give up his stake in the agency. His shares will go into an employee benefit trust to be divided among members of the senior management.
His new-business remit is being taken over by Mandy Nichols, the business development director, who has been with the agency for more than ten years.
Hesketh, Chris Goodwin and Bernie May left the AB Group to set up Advertising Principles 16 years ago. With 143 staff, it is currently the largest independent agency outside London with a client list which includes Dolland & Aitchison, Seven Seas and J D Williams, the direct mail order company.
Hesketh, a psychology graduate, is already an established after-dinner speaker and has formed his own company to pursue more of this work. He will divide his time between the UK and New Zealand where he will live for part of each year.
He said: "This is something I've been thinking of doing for the past five years. I plan to speak about the psychology of persuasion and to explain how selling takes time."