The midfielder joins on a four-year contract after Cardiff accepted an undisclosed offer, and the deal keeps him in the Premier League following City's relegation and QPR's victory in the Championship play-off final.
Mutch, 22, is the third new arrival at Loftus Road this summer following moves for Steven Caulker and Rio Ferdinand.
He said: "I'm really delighted to be here, back in the Premier League.
"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."
Mutch scored seven times in last season's Premier League, and Harry Redknapp said: "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."