The Mali international joins the Championship side on loan until the end of the season.
Maiga, who signed for the Hammers from Sochaux during the summer of 2012, has struggled to make an impact at Upton Park and has netted just two goals in 19 appearances this season.
He told QPR's official website: "It is an exciting new chapter for me. I am here to play games and score goals.
"I am very, very grateful to Harry Redknapp for making this deal happen and I am looking forward to playing for QPR."