Neil Dawson, the agency's executive planning director, has been made the agency's chairman. Both will report to Bainsfair.
The promotions fill the gap left by the exit of Trevor Beattie and Andrew McGuinness nine months ago.
Bainsfair said: "Matt and Neil have done a phenomenal job of keeping the agency on track during a period of change. They have both proved they are enormously talented business leaders and among the most outstanding executives in the industry."
Beattie and McGuinness, the agency's ex-chairman and chief executive respectively, left to set up Beattie McGuinness Bungay with Bil Bungay, its deputy creative director.
Their exit was surrounded by a number of account losses, including Abbey £22m business and the £20m News Group Newspapers brief. Since then, TBWA also suffered lost accounts, including French Connection, Five, Thomas Cook and Ask.com.
Shepherd-Smith was made the sole managing director in January 2005 after Jonathan Mildenhall left the agency.
Shepherd-Smith said: "We have an enviable client list and great people to work with. The challenge is to continue producing the big ideas and great work that are the hallmark of this agency."
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