Brett Gosper, the chairman of McCann Erickson UK, said: "Stephen deserves much credit for leaving the agency in such a great position."
He added: "Chris has played a key role in the development of the London agency in the past three years. Together with Nikki Crumpton, the planning director and Brian Fraser and Simon Learman, the executive creative directors, I think we have one of the most formidable management teams in London."
Macdonald joined the agency in 2005 from Rainey Kelly Campbell Roalfe/Y&R. He was promoted to managing director in 2006.