The 22-year-old, who featured for Switzerland at the World Cup, has penned a three-year deal at the Commerzbank-Arena.
Seferovic only joined Sociedad in July 2013, but his stay in La Liga proved an unhappy one as he scored just twice in 24 top-flight appearances, although he started just nine of those matches.
Despite that poor return, Frankfurt sporting director Bruno Hubner believes Seferovic will prove a valuable acquisition for the Bundesliga side.
"We are delighted that [Seferovic's] move was in our favour," he told the club's official website.
"We chose a young player who has a lot of experience."
After breaking into the first-team at Grasshopper in his homeland, Seferovic moved to Serie A side Fiorentina in January 2010.
He subsequently enjoyed loan spells at Neuchatel Xamax, Lecce and Novara.
