Wallaby great Giteau joins Japan's Suntory
The 34-year-old utility back, who has played 103 times for his country and helped the Wallabies reach the 2015 World Cup Final, is set to join his new team from Toulon at the end of the French season.
Giteau follows fellow Wallaby stars George Gregan and George Smith in joining the Tokyo side after confirming a shock move first rumoured earlier this year.
Scrumhalf Gregan, Australia's highest-capped player, represented Suntory from 2008 to 2011 while flank Smith still plays for the team.
Giteau played a key role in Australia's run to the 2015 World Cup Final, scoring a try that helped knock hosts England out in the pool stage. A head injury cut short his involvement in the final against New Zealand.
Suntory secured a domestic league and cup double last season in Japan, which will host the 2019 World Cup.
Agence France-Presse