Allan takes over for Alexander Schmidt-Vogel, who was tapped by GroupM to take on a newly created role as CEO global trading.
The role marks a return to MediaCom for Allan, who was managing director at UK independent shop TMB when it was acquired by MediaCom in 1999. He then became CEO of the newly combined agency. In addition, from 2003-2005, he was vice chairman of MediaCom Worldwide.
MediaCom became part of GroupM when WPP purchased it three years ago.
Schmidt-Vogel said that "the TMB management was one of the best reasons" that MediaCom acquired it.