Laird, 21, will stay at Loftus Road for the duration of this season, the Championship club said.
Capped by England at under-17, 18 and 19 levels, Laird had loan spells last term with Swansea and Bournemouth.
"It feels brilliant, and I am delighted to get it over the line. I can't wait to get started," Laird told QPR's official website.
"I like to play with confidence and be exciting, and I feel I have the freedom to do that here."
QPR manager Michael Beale added: "Obviously, it is nice to take a boy from Manchester United and for them to trust us with one of their best young players in terms of developing him onwards and upwards.
"He has done really well in the Championship already, and I think he is someone we can be really excited about.
"I like the full-backs to be an addition to our attack, and he provides that. He is very aggressive in terms of one-versus-one attacking, and he is capable of providing assists as well as goals."