In his new role, Cowie will report directly to Rodney Fitch, the founder, chairman and chief executive of PCI Fitch. He will be responsible for a small team at the agency, which specialises in product launches and live events.
Before joining JWT in 2002, Cowie was a board account director at Abbott Mead Vickers BBDO.
He has also worked as the marketing director of Sharepeople.com and before that in the advertising and corporate marketing department at Brunswick PR.
Toby Hoare, the executive chairman of JWT, said: "Peter is a fantastic talent and his contacts list helped to open lots of new doors for JWT's new-business machine. His entrepreneurial skills will be very appropriate for the task at PCI Fitch. I am very sorry he is leaving JWT but would never want to stand in the way of him furthering his career."
The move comes after a difficult year for JWT's London office. It has been hit by a series of international losses, including Persil, Knorr and Axa, amounting to almost £80 million in billings.