After two years of playing with the Western Force in Perth in the Super 14, Giteau is returning to the team that launched his career.
There had been speculation that Giteau, who has scored 343 points in 65 Tests, would take up a big money offer to play in the French Championship with Bayonne after the 2007 World Cup, but that deal fell through.
Giteau, who has played 26 matches for the Force since joining the new franchise for the 2007 season. He will leave at the end of the current campaign and re-join the Brumbies, for the 2010 and 2011 seasons.
"I was very fortunate to have two fantastic offers to consider but, in the end, it came down to a simple desire to return to Canberra," said Giteau.
"Now the decision has been made, it's great to be able to focus entirely on playing for the Force and working hard to break through for our first finals campaign."
The 26-year-old, who has played at outside half, centre and scrum half for the Wallabies, set up the only Force try and kicked the rest of their points in a 16- 10 win over the Cheetahs.