The 23-year-old Ghanaian striker netted 10 goals and provided six assists in 27 appearances in the Austrian Bundesliga this past season.
He was rewarded with a move to an ambitious Saint-Etienne side, who secured their return to the French top division for the new campaign.
Boakye is the Ligue 1 side's fourth signing of the off-season following the captures of Yunis Abdelhamid, Ben Old, and Zuriko Davitashvili.The player recorded a welcome message on the club's Twitter page, saying: "I'm very happy to be here and I can't wait to see you guys in the stadium!"