The deal, worth a reported $2.5 million, comes with eight months remaining on the 34-Test player's contract with the Australian Rugby Union and amid reports of a conflict over third-party payments on his Australian contract.
The 27-year-old Ioane, who is reported to be making $800 000 a year in Australia, would still be eligible to play for the Wallabies against the British and Irish Lions in three Tests in June and July in Australia.
The French season starts in September, although the ARU might not release him from his current contract until late November.
Despite a standoff between the Reds and Ioane's management last week over the alleged third-party sponsorship payments he felt were owed to him, QRU chief executive Jim Carmichael said Thursday it was an amicable departure.
"He goes with our absolute blessing," Carmichael said. "I'm reassured about his feelings toward the Reds and his team-mates and he'll always be a part of the Reds family."
Ioane's place in Australia's 2015 Rugby World Cup team could be in jeopardy as current ARU rules say eligible Wallabies must be playing for Australia-based teams.
He was born in Wellington, New Zealand, but moved to Melbourne with his family when he was 5-years-old.