The Germany international has signed a five-year contract with Frankfurt, whom he helped reach the Europa League semi-finals after joining them for the 2018-19 season.
The French side signed Trapp from Eintracht in 2015 and he won a string of trophies during his time with the capital club, including two Ligue 1 titles.
"I made it clear in the spring that I feel very comfortable in Frankfurt with Eintracht," said Trapp.
"The time in Paris was very exciting, successful and a great experience for me. Now I'm coming home completely and I want to achieve a lot here."
Thank you Kevin! You will always be welcome at the Parc! 🔴🔵🧤 pic.twitter.com/39eOk7daaA— Paris Saint-Germain (@PSG_English) August 7, 2019
Trapp made 96 appearances in his first spell with Frankfurt and featured 45 times last season in all competitions, while he has won three international caps.
"Kevin was an important pillar last season and played a huge part in the positive season we had," said Eintracht sporting director Fredi Bobic.
“He is enormously important to the team and we are very happy to be able to sign a top goalkeeper and German national player for the long term."