Sirigu, who won the most recent of his 28 Italy caps in a win over Lithuania last September, left Genoa upon the expiry of his contract after they were relegated to Serie B last season.
The 35-year-old will be expected to compete with Alex Meret for a starting spot in Naples after David Ospina left for Saudi Arabian outfit Al Nassr, although Luciano Spalletti's men have also been linked with moves for Keylor Navas and Kepa Arrizabalaga.
Sirigu made 190 appearances for PSG between 2011 and 2016, and has also spent time at Palermo, Torino, Sevilla and Osasuna.
Napoli boasted Serie A's joint-best defensive record as they finished third last season, conceding just 31 goals, but have seen the likes of Kalidou Koulibaly, Lorenzo Insigne and Dries Mertens leave ahead of the new campaign.
Napoli travels to Verona for its first outing of the 2022-2023 Serie A season on Tuesday (AEST).