The 34-year-old headed to Canada in February as he searched for game time ahead of the FIFA World Cup in his homeland.
Julio Cesar made seven appearances for Toronto and just as many for Brazil at the showpiece event, which they failed to win.
In a statement on Friday, Toronto general manager Tim Bezbatchenko thanked the shot-stopper for what he had done for the club.
"At Toronto FC we aspire to be internationally recognised as a leader in every aspect that involves our football club, and to be a consistent contender for championships in North America," he said.
"With this ambitious vision comes the need for acquiring players of great character that leave an impact both on and off the pitch. Julio Cesar is certainly one of those players.
"On behalf of everyone at Toronto FC, I'd like to send our sincere thanks to QPR for the opportunity to bring Julio to Toronto.
"We'd also like to thank Julio for everything he brought to our club. He made an immediate impact and all of us are better for it."
Julio Cesar is likely to be competing with Robert Green for the starting spot at QPR, who open their Premier League campaign with a clash against Hull City on August 16.