Matt Giteau in switch to Toulon
Toulon confirmed in a statement he had signed for three seasons, but that the final year was an option.
Giteau had been widely expected to leave Australia after the World Cup, which is being held from 9 September-23 October in New Zealand.
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Hide AdThe 28-year-old will captain the ACT Brumbies in their Super rugby season opener against the Waikato Chiefs in Canberra on Saturday.
Giteau has played 91 Tests for the Wallabies and 89 Super rugby games in two spells for the Brumbies and the Perth-based Western Force. He played in both the 2003 and 2007 World Cups.
Toulon already boast England fly-half Jonny Wilkinson and earlier this month recruited Wales centre and Gavin Henson as wealthy French clubs continue to sign top world talent.
Giteau will also link up with former New Zealand prop Carl Hayman and former Western Force team-mate Matt Henjak at Toulon, who are coached by Phillipe Saint-Andre.