The fantasy drama, starring Peter Dinklage and Lena Headey, is currently airing its second season.
HBO president Michael Lombardo said in a statement: "Series creators David Benioff and DB Weiss raised our expectations for the second season - and then surpassed them.
"We are thrilled by all the viewer and media support we've received for the series, and can't wait to see what Dan and David have in store for next season."
Cast member Charles Dance claimed in December that season three would start filming from mid-May 2012.
The Emmy and Golden Globe-winning show, set in the world of Westeros, centres around a group of people battling to gain control of the Iron Throne.
Game of Thrones airs Sunday nights on HBO at 9pm and Monday nights on Sky Atlantic in the UK at 9pm.
> Game of Thrones Peter Dinklage: 'There's big battles in season two'