The 27-year-old Argentina international has agreed a four-year contract at the Parc des Princes.
A statement on the PSG website read: "This Monday, Ezequiel Lavezzi has been transferred from Napoli to Paris St Germain for the duration of four years. The new offensive asset of the club will wear the number 11 shirt."
Napoli also confirmed the move on their website, adding: "President Aurelio De Laurentiis and everyone associated with the club want to thank 'il Pocho' for contributing to the growth of the team and the achievement of important goals both in Italy and Europe."
Neither club have confirmed a fee but French media suggest PSG have paid an estimated 30 million euros for the South American.
Lavezzi joined Napoli in 2007 from San Lorenzo and last season he helped the Italian outfit finish fifth in Serie A as well as winning the Coppa Italia - their first silverware in 22 years.
Lavezzi, who had been linked with several of Europe's leading clubs, said of his decision to move to France at a press conference on Monday: "I was attracted by the plans at PSG. Here I have the chance to express myself at a club that is on the up and will continue to grow.
"This is a club that will be even more important in the future.
"And then there is the city, everyone dreams of living in Paris.
"There is a great project here, the opportunity to win titles and I want to contribute to that."