Marshall, the chief executive of MediaVest, is expected to become the chairman of the new agency. He will report to Mark Cranmer, the Starcom MediaVest chief executive for Europe, the Middle East and Africa. Iain Jacob, Starcom's managing director, is expected to be the merged agency's managing director.
It is initially expected that, like ZenithOptimedia, the merged Starcom MediaVest outfit will continue to operate from two different offices.
However, it is likely that the merged agencies' resources will be centralised into a single site at a later date.
The news ends months of speculation. It was expected the two agencies would merge last November, but the talks stalled. However, Publicis is now close to concluding negotiations with Bartle Bogle Hegarty, which owns a minority stake in Starcom Motive.
Publicis acquired the majority of Starcom Motive and the whole of MediaVest following the takeover of Bcom3 last autumn. Cranmer said a deal had not yet been agreed.
The two media agencies collaborated to win the £26 million BT press buying account last November.