The 33-year-old was a free agent after leaving Chelsea at the end of last season and impressed Rs boss Harry Redknapp during a trial spell with the London club.
The former West Ham man could make his debut at Blackpool on Saturday and Redknapp has backed his new recruit to make a big impact at Loftus Road.
"Yossi is a good footballer, a top-class player," the Loftus Road boss told the club's official website. "He's got great ability and is someone I have always liked. I actually tried to take him to Tottenham at one time. I think he will be a fantastic addition to the squad.
"We have got a lot of fixtures coming up over the Christmas period and in the New Year, so we are going to need a good squad of quality players for that."
Benayoun revealed that the opportunity to work with Redknapp was a major factor in his decision to join the club.
"I have been training here for two weeks and now I can't wait to get involved and help the team," the midfielder said. "The manager was a very big factor for me. He showed me from the beginning that he really wanted me, and he is someone I have always wanted to play for so I am very happy.
"I have played in the Premier League for the last eight years and I enjoy England very much. The Championship is also a great league and I am looking forward to playing in it and helping QPR build on a great start to the season."