Morton, who has been head of planning since June last year, will take on the position immediately.
He joined TBWA as a managing partner in early 2005, overseeing planning for the John Smith's and PlayStation accounts.
As head of planning, Morton has worked across the agency's E.ON, McDonald's, Nissan and Haagen-Dazs accounts.
Prior to TBWA, he sat on the board of Rainey Kelly Campbell Roalfe/Y&R and worked across a number of Virgin brands.
Morton gained prominence working on Virgin Mobile, which grew from a struggling discount brand to a vibrant youth brand with more than 4m customers.
Morton began his career in advertising as a planner at BMP DDB in 1996, where he worked on Sony, New Labour, Reuters, The Guardian and the National Dairy Council.
Matt Shepherd-Smith, chief executive of TBWA\London, said: "Tom has been a huge asset to the agency since joining us three years ago and he thoroughly deserves this new role".
The appointment comes hot on the heels of Hourston's defection to Grey London as executive planning director.