The appointment will mark the first time Rockstar, the game's developer, has invested its own money in the promotion of its games.
Grand Theft Auto IV will launch on both Microsoft's Xbox 360 and Sony's Play-Station3 on the same day. Previously, the games have always launched on the Sony platform before later migrating to other systems.
Although the game will not be released until October 2007, publicity is expected to begin this September, when the game is announced at the X06 Xbox "brand experience" event in Barcelona.
While McCann Erickson handles the overall Xbox account, the appointment is not believed to have been made through Microsoft. Brian Fraser, McCann's joint executive creative director, is understood to have an existing relationship with Terry Donovan, the son of the photographer Terence Donovan and one of the co-owners of Rockstar.
Advertising for GTA:San Andreas was slapped with a pre-watershed ban by the Advertising Standards Authority in March last year. The ads featured violent content from the game, including the lead character, Carl Johnson, carrying out a drive-by shooting and firing a rocket launcher at a police helicopter.
McCann's latest work for Xbox 360 was generated by its San Francisco office. Microsoft is expected begin a major UK push on its next-generation console in the run-up Christmas.
McCann declined to comment on the news.