The 23-year-old spent the second half of last season on loan at Loftus Road, and impressed sufficiently to earn a four-year deal.
Rs manager Mark Hughes was understandably delighted to finalise the transfer and believes Diakite is a perfect fit for the Premier League.
He told the club's official website: "Samba was a real find for us in January, so we're delighted he's joined us permanently.
"He's a very accomplished footballer and he's made to measure for the Premier League. He's got good pace, strength and ability on the ball and he's going to be a great asset for us going forward."
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And the QPR boss ebulliently claimed that his latest signing can get even better next term, adding: "There's still so much more to come from him.
"He's only been exposed to the Premier League for a handful of games, so I'm sure he's raring to go and get back into the action again."
Diakite could not hide his delight at joining the west London outfit and becoming part of owner Tony Fernandes’ long-term plans.
"It's a dream come true to sign this contract,” the Malian midfielder claimed.
"I loved my time here on loan and I couldn't be happier to join QPR on a permanent deal. It's a fantastic club to play for and the owners have great plans for the future - I am just delighted to be part of it.”
"This is a really exciting move for me."