The Xbox 360 exclusive shooter has sold more than three million copies worldwide in its opening week of release.
The Gears of War series has also topped $1 billion (£639 million) in revenue over its lifetime, and is the first Xbox 360 franchise introduced this console generation to do so.
"Gears of War was the first killer app for Xbox 360, and the series has continued to contribute directly to the overall success of the platform ever since," said Microsoft corporate vice president Phil Spencer.
"Gears of War 3 kicked off the biggest Christmas period in Xbox history, setting the standard for the kind of amazing, action-packed experiences gamers should expect on Xbox 360 this year."
Epic Games boss Mike Capps said that Gears of War 3 is not a finished project, with more content to come with four map packs.
New campaign content will also be available after release, although it will not feature series protagonists Marcus, Dom or Cole.
Gears of War 3 is available exclusively on Xbox 360.
> Read Digital Spy's review of Gears of War 3
> Gears of War 3 launches worldwide: London launch in pictures
Watch the opening sequence from Gears of War 3 below: