Neither PSG nor Benfica disclosed the financial details, but The Athletic reported that the deal was worth around 60 million euros ($66 million) plus 10 million euros in potential add-ons.
A product of the Benfica academy, Neves has made 75 appearances for the club across all competitions and has been capped nine times for Portugal. He won the Primeira Liga in the 2022-23 season and Supertaca Candido de Oliveira last year with Benfica.
"Joao is one of most talented players in Portugal and internationally," PSG President Nasser Al-Khelaifi said in a statement.
"He was so passionate to join PSG and determined to fight for the jersey — which is what we expect of all our players.
"We continue to build a fantastic young team at PSG — based on teamwork, talent and collective spirit — which is the foundation of our club's great future."
