Clarke will oversee a team in London as well as the agency's Vodafone teams across Europe, including Spain and Germany.
The role is newly created and comes seven months after Vodafone shifted its international media planning and buying business from Carat International into OMD.
The account, which involves co-ordinating and buying international campaigns and sponsorship, had been with Carat for five years. It moved after Carat's sister agency, Vizeum, lost the £120 million German Vodafone planning and buying account to OMD.
Starcom appointed Clarke as one of four managing partners a year ago, following a management restructure after the agency dropped the Motive name. Clarke, whose managing partner role included EMEA responsibilities, was previously the international client services director.
Starcom confirmed that Clarke is to leave the agency. Clarke was unavailable for comment.