The Championship club managed by Harry Redknapp secured Keane's services just before the transfer window closed on Friday evening.
Speaking to QPR's official website, the young forward said: "I’m really looking forward to getting started.
"I had a taste for the Championship in a loan spell at Wigan earlier this season, and really enjoyed that. I'm looking to get some more games under my belt, and hoping to help the team get back up to the Premier League.
"I joined because of the manager, he’s very experienced and been successful throughout his managerial career. QPR are also a big club. This is a good challenge for me – and one I’m looking forward to."
Meanwhile, Redknapp enthused: "Will is a young player with fantastic potential. He’s got a good eye for goal, leads the line well and will provide us with good competition in the final third. We’re looking forward to welcoming him into the squad."