Ferdinand confirmed he was to leave United in May after 12 years at the club where he made 454 appearances and won, among other honors, six Premier League titles and the Champions League in 2008.
"QPR was the first professional club to ever sign me. There are great memories for me here – for my family," he told the club's official website.
"I spoke to Harry and [chairman] Mr [Tony] Fernandes at length. I think they both looked me in the eye and knew that I still have something to offer – that I had a genuine desire to come here and play football.
"I had a lot of offers from all over the world – some in places with a better climate than here. But the draw for me was to play in the Premier League and back here where it all started.
"It’s not about money – I had loads of more lucrative offers available to me. I still feel I’ve got something to offer and I’m excited about helping this club cement its place in the Premier League."
Harry Redknapp worked with Ferdinand when the defender was just a youngster at West Ham, and the QPR manager is delighted to be reunited with the player.
"I really couldn't be more pleased," he added. "Rio's a fantastic player and a great professional – I'm delighted we've been able to bring him here.
"I signed Rio as a 14 year-old. He was class on the field and off the field then, and he's continued in that manner throughout his career.
"During his time at Manchester United, he was the best defender in Europe, if not the world.
"To bring him to QPR - when he's still got so much to offer in terms of his quality, class, experience and know-how - is a remarkable coup for the club."