Kranjcar spent last season at Loftus Road, helping the club to achieve promotion, and now returns after the Rs beat the transfer deadline to sign him.
The Croatia international will link up with former Tottenham team-mate Sandro in the QPR midfield, with the Brazilian completing a permanent move to the club earlier in the day, and is delighted to linking up with Harry Redknapp's side again.
"It's a great feeling to be back, it feels like home. I felt a special emotion with the club and the fans," he told the club's official website.
"The fans were phenomenal last season. I had a great relationship with them and hopefully it's only going to get better.
"I really feel happy here, at a club where I really want to play, and I play with all my heart. I can't wait for my season to start with QPR.
"I believe I still have something to prove, for myself and for all the fans. The Premier League is a lot more physical than it was in the past but I'm looking forward to it. I have no doubt this club is going to be in the Premier League for a long time."
Redknapp added: "Niko is a class player. I'm a huge, huge fan of his and really pleased to have him back here."