The Brazil centre-back has signed a five-year contract at the French club as one half of what is set to be the biggest transfer deal of the summer.
Neither PSG nor Milan disclosed any further details regarding Silva's move, but it is anticipated that the 27-year-old will account for a higher proportion of the £50 million fee Milan are expected to get for the star duo.
The other half involves Silva's former Milan team-mate Zlatan Ibrahimovic following him to the French capital.
The Sweden striker is said to be finalising the terms of his move and scheduled to complete a medical later on Saturday.
Milan president Silvio Berlusconi has justified the sale of his two star players just weeks after the club was beaten to the Serie A title by Juventus by claiming that the Rossoneri would save around £120m in fees and by getting them off the wage bill.
Silva becomes the second big-money addition to PSG's squad this summer following the acquisition of Argentina attacker Ezequiel Lavezzi from Napoli.