Dormieux joins in September as managing partner, focusing on the UK side of the business and reporting jointly to EMEA head of the division Jeff Hyams and Mediaedge:cia managing director Tom George.
A spokeswoman for Mediaedge:cia said: "With Jeff looking more at the EMEA, it was felt that the UK side needed bolstering as it is a growing market."
Dormieux, who during his time at Zed Media worked on accounts including Zurich Financial Services, will work alongside Charlie McGee, who also has the title of managing partner.
George said: "Jason not only has a vast amount of experience at a very senior level in the market place across all media channels but also a very broad understanding from brand through to response. He will strengthen our specialist offering and play a key role in integration of these areas within the agency."
This is the latest hiring aimed at ramping up the agency's digital offering and follows the recruitment of former Jupiter Research advertising and marketing analyst Julian Smith to the newly created role of director of digital insight and research in July.
In July, Mediaedge:cia won the £5.5m UK media planning and buying account for games console giant Nintendo.
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