The 17-year-old pop star will be switching on the Christmas lights at both the Shepherd's Bush and new Stratford City centres on 7 November.
He will appear on stage at The Atrium at Shepherd's Bush to count his fans down to the big switch-on before performing four of his singles.
The Never Say Never star will then head across town to the new Westfield Stratford City to launch Christmas in style at the outdoor Chestnut Plaza.
The switch-on will be celebrated with a huge fireworks display over Olympic Park, and the Canadian singer will then perform four more acoustic tracks.
Lucky Bieber fans will also have the chance to meet their teen idol backstage at both events.
Michael Gutman, managing director of Europe & New Markets, said: 'We are incredibly excited that Justin Bieber is launching Christmas 2011 for Westfield London and Westfield Stratford City.
'We want to light up the capital and turn the world’s attention to London with Justin's presence, and make this an unforgettable event for his fans and our visitors.'