The Italy international has been on the books of the Giallorossi, having graduated from the Rome-based club’s academy.
Florenzi spent the second half of last season on loan at La Liga side Valencia after he was not assured of enough playing time under manager Paulo Fonseca.
Paris Saint-Germain have been short at the back since Thomas Meunier left for Borussia Dortmund this summer.
Florenzi will battle it out with German defender Thilo Kehrer, who played at right-back during the final stages of the 2019/2020 Champions League season.
Florenzi will team up with his international team-mate Marco Verratti at the Parc de Princes.
“I’m especially proud and happy to become a PSG player,” the 29-year-old said in a statement on the club’s official website.
“It’s one of the biggest clubs in Europe today, as was confirmed with their run to the Champions League final last month.
“I’ve got the desire to give my maximum for PSG and the supporters of the club. There are enormous challenges ahead of us this season.”
“It will be a pleasure and an honour to turnout at the sides of my new team-mates, who are among the best players in the world.”
Florenzi played 280 times for his boyhood club, scoring 28 goals and proving 32 assists during his time at the Stadio Olimpico.
