The 20-year-old has signed a four-and-a-half-year deal after a reported fee of €30million was agreed between the clubs.
Guedes completed a medical on Wednesday after watching his new team-mates take on Bordeaux in the Coupe de la Ligue semi-final, with the move officially confirmed on Thursday.
“I’m very happy to join such a big club as Paris Saint-Germain,” Guedes said. “Playing here with players of a very high standard will enable me to improve.
“PSG always play to win trophies, so my aim is to win as many trophies as possible, and that PSG keep on winning.
“I know my compatriot Pauleta was well loved by Paris Saint-Germain fans. I hope to do as well as he did, and one day be just as much loved as him.”
“We’re happy to have brought in Goncalo Guedes and want to wish him a warm welcome to Paris Saint-Germain,” added CEO and chairman Nasser Al-Khelaifi.
“Goncalo is a young European talent who fits perfectly with the aims of our project. He’s been followed by numerous European clubs for several years, and he has made the choice to sign for Paris Saint-Germain.
“Goncalo will reinforce the link we have had for a long time with our numerous Portuguese fans in the Paris region, and I’m sure all our supporters will appreciate his technical qualities and his attitude.”
Head coach Unai Emery, who has been seeking competition for striker Edinson Cavani in the January transfer window, praised the versatility of Guedes ahead of his arrival.
“He is a good player, capable of playing wide or in the middle. He is a player of the future who is going to grow a lot,” he said.
Guedes, who has two senior caps for Portugal, has managed seven goals and as many assists in 28 appearances for Benfica this season.
He had been linked with a possible move to Manchester United, although interest from Jose Mourinho’s side never materialised.