The move will formally take effect on Friday, and Morrison is expected to make his QPR debut against Charlton in the Sky Bet Championship on Saturday.
"I just want to help QPR get to the Premier League - that's my only objective during my time here," said the England Under-21 international in a statement released by QPR.
"If we manage to do that, it would be great for everybody connected with the club.
"All I want to do is play football. I just want to show everyone what I can do week in, week out.
"The aim here is to get the club promoted and I want to contribute in helping QPR to get there."
Morrison, 21, progressed through the ranks at Manchester United and made three senior appearances for the Red Devils, all in the League Cup.
He moved to West Ham in January 2012 in a £650,000 deal and has made 22 appearances for the Hammers, scoring five goals.
West Ham announced on their website they will have the option to recall Morrison after 28 days of the loan.
QPR manager Harry Redknapp is also hoping that Morrison can help the Hoops in their promotion bid.
"Ravel is fit and ready to play and I'm hoping he can come in and make an impact," said Redknapp.
"He's got fantastic ability, there's no doubting that. He's got great pace, can dribble and score a goal.
"If we can get the best out of him, he could make a big difference.
"He's certainly a talented footballer - he's just got to step up now. He's got to come here and show what he can do consistently. He's got everything.
"We're pleased to have him here."