The 19-year-old centre-back moves from Serie A club Roma and has signed a five-year deal at the Parc de Princes.
No fee has been officially disclosed but it has been reported the Marquinhos has cost big-spending Les Parisiens in the region of 35million euros (£30.1million).
A statement on www.psg.fr read: "Paris Saint-Germain is delighted to announce that Marcos Aoas Correa, known as Marquinhos, has signed a five-year contract with the club after transferring from AS Roma."Marquinhos becomes PSG's third major signing of the week following striker Edinson Cavani and left-back Lucas Digne, who have both also signed five-year contracts in the French capital.
"The transfer of Marquinhos, a future star whose qualities have already attracted the attention of Europe's biggest clubs, is a source of great satisfaction for Paris St Germain," said club president Nasser Al-Khelaifi.
"It underlines the club's desire to look towards the future in order to construct one of Europe's biggest clubs."
Marquinhos only joined Roma last summer after coming through the youth system at Corinthians in his native Brazil.
The defender went on to make 26 Serie A appearances in his debut season outside of South America and made such an impression that he was linked with moves to Manchester United and Barcelona.
But PSG have won the race for his signature as new boss Laurent Blanc looks to defend the French title which was won for the first time in 19 years last season and launch an assault on the Champions League.
"I am delighted to be joining Paris St Germain, a club where so many Brazilians have played and helped write the club's history," said Marquinhos.
"I will do everything I can to continue that tradition and write my own name into the club's illustrious history books.
"Paris St Germain will help me continue my progression alongside exceptional players, with the desire to win trophies and also win the hearts of the supporters."