The 20-year-old Italian striker, who has made just six first-team appearances for United this term, will hope to become a regular under R's manager Neil Warnock as the West London club strive to stay in the Barclays Premier League.
Macheda will wear the no.33 shirt at Loftus Road and told QPR's official website that he's determined to make his mark at the club.
"I was attracted by the challenge and by the players that QPR brought in during the summer," Macheda said.
“There are some very big players at the club now and I am really looking forward to training and playing with them. I also know the fans are very, very passionate, and this interested me also.”
Rangers boss Warnock was delighted to secure Macheda's services but stressed his belief that Macheda's long-term future lies with Manchester United.
"This is a great opportunity for both parties. Federico is not getting a regular game at United
Debut: v Villa, 5 April 2009
"I was attracted by the challenge and by the players that QPR brought in during the summer." - Federico Macheda