Company head of PR Asam Ahmad said H&K would also handle press office work, having decided against his original plan, made at the time the pitch process began three months ago, to hire separate agencies for the two remits.
Ahmad said: "H&K will promote individual games, but if a game requires additional creative input I may draft in other agencies."
H&K replaces Bell Pottinger Consultants, which had been retained since 1999.
Last month it was revealed that Sega was talking to agencies about its multimillion-pound pan-European advertising and media accounts as it prepares to bring its marketing and distribution functions back in-house.
Sega Europe has repositioned itself as a software publisher, having quit the hardware market two years ago, following disappointing sales of its Dreamcast console.
Ahmad said he had narrowed "more than 30" initial expressions of agency interest in the corporate and press office contract down to nine, before seeing pitches from four. Eventually just two agencies were in the running for the business.
H&K's consumer tech team, led by senior associate director Sam Clark, will handle the account, with strategic advice from MD Sally Costerton’s corporate comms team.
Upcoming games to be launched by Sega Europe and H&K include Billy Hatcher and the Giant Egg, which will launch in November.
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