The Argentina international was on a season-long loan deal at the Parc des Princes, with PSG holding the option to sign him permanently at the end of the season.
Icardi has scored 20 goals in 31 appearances across all competitions for Thomas Tuchel’s men, including five in six Champions League games. PSG are still in the competition after holding off the challenge of Borussia Dortmund in the round of 16 stage.
Icardi’s 12 goals in the French Ligue 1 helped PSG retain the title after the season was ended early in France because of the Coronavirus pandemic.
An official announcement from PSG reads: "Paris Saint-Germain are delighted to announce the signing of Mauro Icardi on a permanent deal, following the striker’s loan from Inter Milan during the 2019-2020 season.
"The Rosario-born player is the 16th Argentinian player in the history of Paris Saint-Germain, and has made 31 appearances for the Rouge et Bleu in the 2019-2020 season, picking up a Ligue 1 winner’s medal, scoring 20 goals and providing four assists."
Icardi spent six successful seasons at Inter Milan after joining from Sampdoria in 2013 but his final few months at the San Siro was riddled with controversy when he was stripped off the captaincy.
A statement from Inter Milan confirming the departure of the 27-year-old read: 'FC Internazionale Milano announces the transfer of Mauro Icardi to Paris Saint-Germain FC: the striker, born in 1993, has permanently moved to the French club.
'The Club thanks the player for the six seasons he spent with us and wishes him the best for his future professional career.'
