
Steward has been at the agency since March, joining from Rainey Kelly Campbell Roalfe/Y&R after 12 years.
He will report to Michael Islip, the chief executive for the UK arm of the agency. Islip was the managing director before taking on this role in March.
Islip said: "Matt has first-rate experience of working at the most senior level with some of the most exciting brands in the UK, and is perfectly placed to help drive our business forward."