The appointment is the first senior hiring from the McCann executive planning director, Nikki Crumpton, since she joined the agency from Fallon last August.
Before his stint at Mustoes, Clements spent three years at M&C Saatchi as the group planning director on Scottish Courage, Lucozade and Privilege Insurance. Before joining M&C Saatchi, he worked at Banks Hoggins O'Shea, Bartle Bogle Hegarty and Heresy.
Crumpton said: "David's experience across a wide range of brands and planning challenges contribute a welcome addition to our agency. An ability to view problems from all angles, a desire to throw himself at any challenge, and all carried out with the driest sense of humour, make him perfect for the job."
Clements' is the latest senior departure at Mustoes. In February, the managing director, Ben Simonds-Gooding, left to buy the headhunter Braverman. The previous August, Mick Mahoney left his position of executive creative director at the agency to join BBH as a creative director.