The 32-year-old has signed a four-year contract that will keep him at Loftus Road until the summer of 2017.
"It's fantastic that we've been able to attract a keeper of such outstanding ability to the club," said QPR boss Mark Hughes.
"When the opportunity to sign a player of his quality presents itself, you have to act quickly and we've managed to get the deal done.
"It was always my intention to bring two goalkeepers to the club this summer and now we've got fantastic competition in that department."
He added: "He's an outstanding individual, as well as being an outstanding player.
"Not only will we benefit from his ability, but we'll also benefit from his experience and winning mentality."
Cesar said: "I'm so happy and excited to be here.
"The ambition of this club was presented to me by the chairman and the coach and I couldn't have been more impressed.
"The desire to achieve things at this club is clear for everyone to see and I wanted to be part of that. I have come here to compete for the shirt and give my all."
Cesar added: "The English Premier League is the best division in the world.
"Everyone wants to play here and I am no different. Now I just want to give my all to the club and show the fans what I am capable of.
"This is a really exciting move for me and I can't wait to get going."