Hall, who has been on trial at Loftus Road over the summer, has put pen to paper on a two-year contract.
The 23 year-old was registered prior to the midday deadline and is therefore expected to go straight into the Hoops squad for Saturday’s Sky Bet Championship opener against Charlton at The Valley.
QPR head coach Chris Ramsey told qpr.co.uk: “I’ve always liked Grant from when I worked with him at Spurs.
“He’s an old fashioned defender – he can head the ball, he can tackle and he doesn’t mind putting his foot in when he needs to. But he can play as well from the back, and that’s what we’ll be looking to do when the opportunities present themselves this season.
“He’s still a young boy and centre-half is a very responsible position, but he’s got experience in the Championship and that’s vitally important for us.”