The 35-year-old Ferdinand signed a one-year contract with the London club to be reunited with Harry Redknapp, his first manager at West Ham.
The former England captain, who played 81 times for the national team, has been a free agent since he was released by United in May after making 454 appearances during 12 trophy-filled years at Old Trafford.
"I had a lot of offers from all over the world — some in places with a better climate than here," said Ferdinand, who went to QPR games as a child. "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."
Ferdinand's break in football came under Redknapp at West Ham before leaving in 2000 for Leeds, where he spent two years before signing for United.
"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," Redknapp said. "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."
Ferdinand is QPR's first signing since the club returned to the topflight in May after winning the League Championship playoff.
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