His arrival in Turin comes after the club opted not to pursue a permanent deal for Joe Hart, who spent last season on loan from Manchester City.
Sirigu, who has won 17 caps for the Azzurri, returns to Serie A five years after leaving Palermo for PSG.
The 30-year-old told the official club website: “I am very happy to be part of this club. I chose Toro because they wanted me strongly and have a sound project in place to grow over the coming years.
“The club and the president made me feel important and I thank them for that. I am honoured to be part of a club that has a unique story.”
The Italian goalkeeper won four Ligue 1 titles, two Coupes de France and three Coupes de la Ligue with PSG but lost his place to Kevin Trapp last season, spending much of the campaign on loan at Spanish sides Sevilla and Osasuna.