The Dutch striker, who only scored once for Norwich City last season, will spend the upcoming campaign with the Ligue 1 outfit.
The Dutchman arrived at Carrow Road for a reported 10.7 millon euros from Sporting at the beginning of last season, but failed to live up to the price tag as he netted just once in 25 Premier League appearances.
And, following the club's relegation, Norwich has decided to offload Van Wolfswinkel for the duration of the 2014-15 campaign.
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"I am very happy, I really wanted to sign here," the 26-year-old told Saint-Etienne's official website. "The management, the coach, the people who work at the club have given me reason to want to join Saint-Etienne. I was able to talk with the coach and I look forward to working with him.
"Saint-Etienne are one of the largest French clubs. Last year, the coach and the team achieved very good results. Finishing fourth in the championship of France is not easy. My goal is to work hard for the team and to be important for the club."
Norwich manager Neil Adams added: "I can't speak highly enough about how professional Ricky has been even though he had a difficult first season at the club. His attitude has been first class, and this move represents an opportunity for him to play regularly and get back to scoring goals in the way he has done in the past. We wish him the best of luck."
Norwich also confirmed the signing of Gary O'Neil on a two-year contract on Tuesday, after the midfielder was released by Queens Park Rangers.