The experienced forward was released by Glasgow Warriors and has signed a two-year deal with the Pro D2 club.
Harley, 32, is Glasgow’s appearances record holder and was part of the side that won the Guinness Pro12 in season 2014-15.
It was announced in March that he would be leaving his only professional club and he said at the time that he saw his future in France.
“I think France would be cool – a different culture and a different language,” Harley said. “I studied French in school a fair bit and I’ve tried to keep it up, although I wouldn’t say that I’m fluent. I think having the language, though, would help ease the transition if I was to go there.
“When we’ve played French teams in Europe I’ve seen a hard, physical edge to their game. So if that’s where I end up playing it would be interesting to see that and take on that challenge.”
Harley, who can play in the back row or at lock, played 267 times for Glasgow and has been capped 23 times by Scotland, his last international appearance coming in the win over Tonga in the Autumn Nations Series last October.