French club Nancy indicated on Sunday night that the 23-year-old was on his way to Loftus Road and the Rs have now confirmed the Mali international's signature.
Diakite has joined on loan until the end of the season when QPR have the right to make the transfer permanent.
"Samba is a young player who has made an impression on French football," QPR manager Mark Hughes told the club's official website, www.qpr.co.uk. "There has been a lot of interest in him from top clubs in France so we have done really well to get him in.
"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."
Diakite is currently on international duty at the African Nations Cup but flew to London for a medical on Sunday afternoon, with the required paperwork completed this lunchtime.
"It is a dream to join a Premier League club," Diakite said. "The board and the 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 African Nations Cup and give my all for the club. It is a very exciting move for me."
Diakite becomes manager Mark Hughes' third signing since taking over from Neil Warnock at Loftus Road, following the arrival of AC Milan left-back Taye Taiwo and Manchester City's Nedum Onuoha. Manchester United striker Federico Macheda arrived on loan earlier this month during Warnock's reign.
Source: PA
Source: PA