Thomas, who joined Cake from Frucor Beverages, where he was marketing manager for energy drink V, was unavailable to comment. It understood he has taken soundings over a number of opportunities although he is not thought yet to have a specific job to go to.
Cake chief executive Mike Mathieson said, in a statement: 'Darren joined us with a clear challenge ahead of him - to ensure we operate to the best of our ability as a creative consultancy.
He added: 'Having worked directly with Darren in his role at Danone for several years, his previous experience was hugely appealing, offering us that unique client perspective.
Mathieson, who assumed the CEO position when Thomas joined Cake, said he would 'miss the intelligence, charm and wit Darren brought to Cake. He deserves every success for the future.'
Thomas's first contact with Cake came while working at Danone Waters, when he appointed the agency to work on a youth marketing programme for mineral water brand Evian.
In a separate move, European senior account manager Kat Thomas (no relation) has also quit the agency.
Thomas is moving to Sydney, Australia, for 12 months and plans to remain in PR, working as either a freelance PRO or for a PR agency.
Thomas, who joined Cake three-and-a-half years ago, said she planned to return to London in 2005, adding: 'There's no other agency in London for me than Cake'.
Thomas manages the agency's European brief for Nintendo. She said responsibility for that account would be carved up internally.