MacCallum, who joined the agency as a director at the end of its first year in 2004, has been the managing director since 2008. In another promotion, managing partner Sam d’Amato has become the chief strategy officer.
Philippa Brown, the chief executive of Omnicom Media Group, said: "Alistair not only played a formative role in the agency’s early years but has led its progression from a small agency to a highly respected scale agency that is truly coming of age, and he thoroughly deserves his promotion to CEO."
Before M2M, MacCallum was a board director at UM London and CDP. He started his media career at Zenith Media in 1996.