The 29-year-old Trapp spent last season on loan at Frankfurt after falling further down the pecking order in Paris following the arrival of Gianluigi Buffon.
Reports in Germany said the transfer fee was around seven million euros ($7.9 million) for Trapp, who helped Eintracht reach the semi-finals of last season’s Europa League.
Following Buffon’s decision to rejoin Juventus this summer Trapp was expected to serve as back-up to first-choice goalkeeper Alphonse Areola at PSG.
Trapp, who has three caps for Germany, won two Ligue 1 titles with PSG as well as both the French Cup and French League Cup three times.
