Mischief won the account following a six-way pitch. A huge 12 agencies were initially asked for credentials.
The agency's first task will be to launch The Sims 3 in the mainstream press from 1 April. Work with specialist media on the game has already begun.
Shine Communications, the incumbent, will continue to work with Electronic Arts on all the EA Sports and EA Games areas of the business.
Shine Communications founder Rachel Bell also has a small equity stake in Mischief, although the agency is run independently.