Benfica striker Ramos signs for PSG
Ramos, 22, came through the Portuguese club's academy and scored 19 league goals in 30 matches last season.
At the 2022 World Cup he scored a hat-trick and made an assist in his first international start in the last 16 win over Switzerland.
"It's a big moment of pride and immense joy to join Paris Saint-Germain," Ramos said in a PSG statement.
"PSG are one of the biggest clubs in the world with one of the best squads," he added.
Ramos is the Parisians' eighth summer signing after the arrivals of the likes of France defender Lucas Hernandez and Spain attacker Marco Asensio.
They missed out on Harry Kane with the England striker being heavily linked with Bayern Munich.
PSG open the defence of their Ligue 1 crown by hosting Lorient on Saturday but the start of the campaign is being clouded by questions over Kylian Mbappe's future.
The France captain has one year left on his contract with PSG, who want him to leave now rather than for free next summer.
Mbappe is refusing to sign a new contract and PSG believe he has already struck a deal to move to Real Madrid next year.
The standoff between the 24-year-old and the French club reached a new peak last month when they dropped him from their squad to tour Japan and South Korea.
Mbappe has been training with the reserves in preparation for the new term.