Thiago Silva, 27, has signed a five-year contract, PSG said without revealing the size of the transfer fee.
The player is currently in his homeland as he prepares to appear in the Olympics in London.
PSG coach Carlo Ancelotti said he was delighted to have wrapped up a key signing.
"I am very happy with the arrival of Thiago Silva. He is a fantastic player. Everyone knows he is one of the best defenders in the world."
PSG, runners-up last season to Montpellier in the French league, are also targeting AC Milan's Swedish striker Zlatan Ibrahimovic.
"There is no agreement as yet - we are still working on when everything is sorted out we will have a press conference," Ibrahimovic's agent Nino Raiola told AFP.
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