Mawhinney will oversee the creative division and take part in a restructure of the department following the imminent departure of the agency's creative director, Gary Setchell, who is leaving to become a teacher.
He joined BJL is March 2008 where he was tasked with running the agency's creative department and also took a place on the board.
Mawhinney has also worked at Bartle Bogle Hegarty, CDP, Still Price Lintas, Ogilvy & Mather and Faulds.
Dean Lovett, chief executive of McCann Erickson Central, said: "Mawhinney's arrival is part of a huge investment to ensure we continue to develop our creative product. Our aim is to provide our clients with award-winning creative which will help their businesses to grow."