The 23-year-old has signed on an initial loan deal but there is an agreement in place for a permanent transfer at the end of the 2011-12 season.
Diakite is currently on international duty with Mali at the Africa Cup of Nations, but flew into London on Sunday to complete a medical before putting pen to paper on Monday afternoon.
"It is a dream to join a Premier League club," Diakite told QPR's official website. "The board and manager have big ambitions to achieve and I am delighted to join a club with such goals. I have always enjoyed watching English football and I can't wait to return from the Africa Cup of Nations and give my all for the club. It is a very exciting move for me."
QPR manager Mark Hughes expressed his delight at the signing, insisting that several top clubs had been in the race for Diakite's signature.
"Samba is a young player who has made an impression on French football," Hughes told the club's official website. "There has been a lot of interest in him from top clubs in France so we have done really well to get him. He is a good age, has got strength, power, can carry the ball and can score goals from midfield on occasions. He will give us more physical presence and athleticism in the middle of the park so he is going to be a good addition."
Get more transfer news with Goal.com's LIVE! coverage.