The midfielder becomes the club's third signing of the summer and returns to the Premier League following the Bluebirds' relegation to the Championship in 2013-14
The 22-year-old midfielder has signed a four-year contract with Harry Redknapp's side, and becomes the club's third signing of the summer following the arrivals of Rio Ferdinand and Steven Caulker, while Redknapp is also keen to secure a deal for Juventus' Mauricio Isla.
“I’m really delighted to be here, back in the Premier League," he told the club's official website.
“I don’t see a better place for me than QPR at the moment. The club is heading in the right direction and I’m really excited about the season ahead.
“I thought I had a good first season in the Premier League last year with Cardiff, so I was delighted when QPR came in for me and offered a route back to the top-flight.
“I’m really happy to be here and hopefully we can do well this season”
Redknapp added: “Jordon’s a fine young player, with a big, big future.
“He’s already shown what he can do at this level with Cardiff last season with a decent goals return – and this move will provide him with a great platform to take his game on to the next level.
“He wants to learn and improve his game. He’s a good pro with a great attitude and this is a big opportunity for him at QPR.”