The 31-Test Wallabies star inked a three-year deal with the Los Angeles Chargers earlier this year but was waived and placed on the injured reserves list.
A hamstring injury was behind the 25-year-old, two-time World Cup talent's fall from grace at the Chargers.
He'll be back in action in the Top 14, due to arrive in the south of France by October.
Petaia had left long-time Super Rugby club Queensland Reds with their blessing and the nine-month deal leaves his options open ahead of the 2027 World Cup on home soil.
But the lucrative R360 competition could also be an option for Petaia, the youngest Wallaby to play at a World Cup, should the concept eventuate.
Former Wallaby and Rugby Union Players' Association boss Justin Harrison described Petaia as an "outstanding talent" and anticipated RA would at least attempt to lure him home.
"A huge amount of resources that he's given to Australian rugby. We've also put into him," Harrison said on Stan Sports before the announcement on Wednesday.
"He's benefited now from understanding a different type of ecosystem and the hierarchy of a different sporting infrastructure and probably realising that he's in a good environment back here in Australia as well, and he's got a great opportunity now to head into a home World Cup.
"There has to be timing and there has to be the right amount of trust and honesty and a plan put in front of him."
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