The 20-year-old, who signs from Rosario Central has made 36 appearances for the Argentinian club, scoring two goals and setting up another nine.
Lo Celso told Paris Saint-Germain's official website: "I'm delighted to have signed for Paris Saint-Germain. I will soon join one of Europe's most important clubs with a squad comprising numerous great players, including my compatriots Angel Di Maria and Javier Pastore".
The youngster will spend the first half of the coming season on loan at Rosario Central as part of the deal.
PSG confirmed the move with the following tweet.
PSG sign Argentine midfielder Giovani Lo Celso to five-year contract https://t.co/FeWdmTYFgB pic.twitter.com/BdS37L12Nj
— PSG English (@PSG_English) July 26, 2016