Millar replaces Fiona Blades. She has reduced her role to three days a week - working mostly on Mercedes - to allow her to focus on a research project she is pursuing outside the agency.
In his new role, Millar will use his digital background to underpin Claydon Heeley's strategic credentials.
The appointment is part of the agency's reorganisation, which aims to place digital at the heart of all of its communications. This began last year in a restructure that saw Claydon Heeley and Agency Republic joining the sales promotion agency Alcone and the software company Code in a new group structure called Zulu.
Millar will report to Martin Brooks, the chief executive of Zulu. He will be briefed to develop closer links between Claydon Heeley and the other agencies in the group.
Brooks said: "Given Tim's four-plus years' intimate knowledge of digital, he becomes a vital ingredient in the glue that bonds the Zulu proposition together.
"This gives him a unique opportunity to inject digital understanding and integration into Claydon Heeley Jones Mason."
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