Morton will take responsibility for planning and developing strategy across Publicis London, Publicis Modem, Publicis Dialog and Publicis Blueprint.
It is the first time that Publicis has appointed a chief strategy officer to work on all of its group businesses, and follows news earlier this month that Andy Lear, the head of planning at Publicis London, was leaving the agency to become an advertising consultant.
Nigel Jones, the Publicis Group UK chairman and chief executive, said: "We're bringing all the brands and disciplines in the group closer together and planning will be the glue. Tom is one of a very select few who have the experience and ability to do this."
Morton had been at TBWA\London for five years, initially joining the agency in 2005 as a managing partner. He became the chief strategy officer in 2008, and has been responsible for working on brands including Sony PlayStation, Nissan and Adidas.
He is also currently working on a book based on his social media alter-ego, Dr Johnson.
Before joining TBWA, Morton worked at Rainey Kelly Campbell Roalfe/Y&R and DDB London, and in 2001 was named by Campaign as a "Face to Watch".