McPartland steps in following the departure of Leroyson Figueira, who is now a freelance digital and social creative director.
At Mother he launched Mother Experience, a production unit creating work for brands including Stella Artois, Dell, Pimm’s, Becks, Acer & Pot Noodle.
Mark Whelan, global creative director and founder of Cake, said: "Bringing Dermot in is key to the direction we and our clients are taking at Cake. We need to continue to build on our success in connecting brands with their audiences through innovative content, digital campaigns and live experiences, and Dermot brings solid experience and vision with him in these areas."