McTear joins as a creative director across the agency's accounts. Steiner will fill a new role, working with the executive creative director, Richard Flintham, to produce long-form content alongside TV and digital campaigns. His appointment does not affect the joint heads of TV, Nicky Barnes and Charlie Orr.
The Fallon managing director, Karina Wilsher, said: "Tony and Rob both have incredible creative energy and ambition. That's what makes them feel instinctively Fallon. It's a great time for us to have even more talent on board."
"There's an incredibly high bar at Fallon, that's why I want to work there," McTear added.
McTear joined TBWA\London in 2004 and won the Grand Prix in Cannes that year with "mountain" for Sony PlayStation 2 before quitting in June 2007 without a job to go to.