The Moroccan international passed a medical on Tuesday and has now finalised a deal which keeps him in the Premier League following Rangers' relegation.
The move reunites Taarabt with Martin Jol, who was manager at Tottenham during his time at White Hart Lane.
"This was a difficult decision for me, but at this stage of my career I feel I need to be playing at the top level," he said.
"I hope the fans understand my decision and I really hope to return to Loftus Road one day. I wish QPR well for the season and hope they achieve promotion back to where I believe the club belongs."
Jol said of Taarabt earlier this week: "I like his creativity and, of course, sometimes it comes off and he scores a lot of goals.
"It is like (Fulham forward) Dimitar Berbatov. Sometimes these fantastic talents will be blamed but I hope to find a way to gel him in together with the boys we've got.
"I think he can do a hell of a job for us because he is a tremendous player on the ball."