Clark announced he was leaving Cohn & Wolfe last week after five years at the agency (PRWeek, 16 May).
It has since emerged that Huntsworth has brought him on board to develop the agency's pan-European medical comms portfolio.
Clark starts in the newly created role on 2 June and reports to chief executive Sandy Royden.
Clark was joint-MD of Cohn & Wolfe's London healthcare division before moving to the US in September 2006 to become MD of the New York healthcare arm.
He returned to the UK after less than a year to take on its business development director role and has been handling work for flagship clients including Astra-Zeneca and Roche.
Huntsworth's medical comms associate divisional director Annabelle Sandeman has been promoted to divisional director medical comms.
The agency has also appointed former Novartis global brand communications manager Jason Coulls as account director and former Roche group product manager Amber Fensome as senior account manager.