The 34-year-old moved to the MLS in February after struggling for game time under Harry Redknapp, with Rob Green preferred as the club secured an immediate return to the Premier League.
"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," general manager Tim Bezbatchenko said in a statement.
"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."
The move comes as no surprise, with Toronto head coach Ryan Nelsen previously indicating that Cesar would return to England after the World Cup.
Green signed a new two-year deal with the R's in July with Cesar's future at Loftus Road unclear after playing just one game last term.