Mahoney will lead O&M’s UK creative department, working with clients including Pizza Hut, the government and BP. He will report to the chief executive, Charlie Rudd.
Before working at RKCR/Y&R between 2013 and 2015, Mahoney was the executive creative director at Havas Worldwide London for four years. He has previously worked with Rudd while at Bartle Bogle Hegarty.
Rudd said: "When I knew there was an opportunity to bring in a new chief creative officer, the person who was top of my list was Mick.
"He is the epitome of a future-facing chief creative officer – collaborative, channel-agnostic, idea-obsessed and highly ambitious."