Business development director Clark is believed to have another job lined up but would not disclose where he is headed.
Clark joined C&W as director in 2003 after a stint as an associate director at Weber Shandwick and three years at Munro & Forster Communications.
He was made joint-MD of the London healthcare division alongside Jacinta Collins before moving to New York.
He moved to the US in September 2006, to become MD of Cohn & Wolfe's New York healthcare arm (PRWeek, 29 June 2006). He replaced agency stalwart Jennifer Gottlieb who had joined US-based healthcare specialist agency WeissComm Partners earlier that year.
Clark took on the role of global healthcare practice leader in the US with a brief to grow C&W's healthcare offering, reporting to global CEO and president Donna Imperato.
However, Clark returned to the UK after less than a year. He rejoined the London office and handled work for flagship clients including AstraZeneca and Roche. He said the move had only been a temporary position.
Clark's departure coincides with the arrival of Freud MD Fiona Noble as CEO this summer (PRWeek, 8 February). C&W's hunt for a CEO began after Jonathan Shore's exit last November, following a five-year stint at the helm.