The 26-year-old forward cost the Ligue 1 title-holders a reported 50 million euros.
"Paris Saint-Germain is delighted to announce it has secured the services of Ferran Torres. The Spanish World Cup-winning forward has signed with the Club until 2031," read the club statement.
The former Valencia and Manchester City star is reunited with PSG coach Luis Enrique, who as Spain coach gave him his international debut in a Nations League match against Germany in 2020.
"Ferran is a top-class international player, who we know really well," Luis Enrique told the media on Saturday.
"I think he will adapt perfectly to what we want him to do.
"He is a player who can play anywhere in attack.
"We have players who have or are leaving, so it is important we find this type of player."
Torres, who also won EURO 2024 with Spain, said PSG had not lost their hunger for success despite winning back-to-back Champions League titles.
"I'm delighted to be beginning a new adventure at such an ambitious club as Paris Saint-Germain," said Torres in the club statement.
"I'd like to thank President Nasser Al-Khelaifi, Luis Campos and coach Luis Enrique for giving me the opportunity to join the team, which I hope to help win as many trophies as possible."
Torres, who won three LaLiga titles while at Barcelona, came on as a substitute in the World Cup final and scored in extra time to dash Argentina's hopes of retaining their title.
He joined Barcelona from Man City in the January 2022 transfer window.
Torres went on to score 65 times in 207 appearances for the Catalan giants, including in the Copa del Rey final victory against Real Madrid in 2025.
"The club would like to express its gratitude to Ferran Torres for his commitment over the last four and a half seasons as a Blaugrana and wishes him all the best for the next stage of his professional career," said Barcelona in a statement.
His arrival in the French capital may raise Premier League side Liverpool's hopes of signing PSG's 23-year-old winger Bradley Barcola, who sparkled for France at the World Cup.
The two clubs have been in discussions for weeks, with PSG's apparent asking price of around 150 million euros ($173 million) proving the stumbling block.
As the summer transfer window ramps up, Flashscore has everything you need to keep up with breaking news, rumours and analysis. Follow our live transfer blog to follow the biggest moves, whilst expert Dean Jones will be on hand to provide the inside stories from around the world.