Buckley, who played Jay in the popular Channel 4 comedy series The Inbetweeners and two follow-up movies, was chosen as Game’s brand spokesman after building a YouTube following with his own gaming channel, Completed it Mate.
In the launch video, created by 101, Buckley tells his subscribers how he is proud to be a "sellout" after agreeing to help the brand sell computer games.
As the campaign unfolds, Game will make further demands of Buckley, including taking over his room with branded paraphernalia, across 13 TV and video-on-demand spots from today (Thursday) until Christmas.
Game is also using print and social media to build an army of "sellouts" – gamers with YouTube or Twitch channels who will be given the chance to promote the retailer by creating their own branded videos in return for cash and other rewards.
The "Sellout" campaign was created by Ryan Delehanty and Ben Williams. 101 picked up Game’s ad account in 2014 after a competitive pitch against three other agencies.
Game’s previous marketing activity includes the Christmas Shopping Simulator, a downloadable tongue-in-cheek game, which competed with festive heavy-hitters such as John Lewis in terms of YouTube views in 2014. The game went viral, boosted by YouTube stars including PewDiePie. A sequel for Black Friday was also a hit last year.
Nicole Burdett, head of marketing at Game, said the change in strategy reflects the brand’s desire to be overt about its paid relationship with a YouTube influencer, which "allows us to have fun with our audience".
She added: "There will be plenty of Christmas campaigns featuring celebrities – but we’ve gone for James because he’s a gamer.
"For the first time, we’re seeing YouTuber conventions break through into traditional media."
The simulator games project followed Game floating on the London Stock Exchange, and the promotion of insight and reward director Fred Prego to marketing and insight director, in 2014.