The 35-year-old centre-half, released by Manchester United at the end of last season, has signed on a one-year deal following a series of talks with the west London club.
Ferdinand spoke with Rangers boss Harry Redknapp earlier this week following his return from TV punditry at the World Cup and completed a medical on Thursday.
He becomes the newly-promoted club’s first signing of the summer transfer window.
“I spoke to Harry and Mr Fernandes at length. They both looked me in the eye and knew that I still have something to offer,” Ferdinand told the club’s official website.
“It’s not about money – I had loads of more lucrative offers available to me, 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.
“I still feel I’ve got something to offer and I’m excited about helping this club cement its place in the Premier League."
Ferdinand trained with QPR as a youth before joining West Ham’s academy in 1992 where he broke into the first-team under Redknapp – then manager at Upton Park.
His brother Anton enjoyed a two-year spell at Loftus Road while his cousin Les, the former England and Tottenham striker, is considered a QPR legend by supporters.
And Ferdinand said: “My dad used bring me here as a young boy and I used to sit in the Loft.“QPR was the first professional club to ever sign me and there are great memories for me here – for my family.
“Anton had nothing but good things to say and I watched here when I was a boy, with the likes of Ray Wilkins, Clive Wilson, David Bardsley and Alan McDonald.”
Ferdinand was released by Manchester United after a 12-year stint at the club, winning six league titles and the Champions League among others, while also playing over 400 times for the club.
He brings the experience boss Redknapp has identified as key to Rangers pursuit of Premier League survival this season.
And Redknapp told Sky Sports News: "We were the only club he was looking to join so it wasn’t that tough a deal to do.
"Rio is easy to deal with and his demands weren’t great. He just wants to play football for another year and we couldn’t be happier. He’s a great signing for us.
"Players like Rio don't come along too often. I said when he was a youngster he would be one of the best defenders in Europe and he has been over a number of years.
"For me, he's a class act on and off the field and he'll be a great influence for everyone at QPR."