Mitchell, who replaces Laurent Boninfante, will report into head of OMD group digital, UK, Matt Simpson.
Mitchell was previously a senior strategic planner with The Search Works, the digital marketing company. He has also had experience of running his own business.
His new role will include developing OMD's strategic approach to search, as well leading new business pitches.
He will work across OMD UK, Manning Gottlieb and OMD International.
This article was first published on Media Week