The Netherlands international will take the No.10 shirt at Loftus Road following a campaign with Norwich that ended in relegation.
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Fer told the club's official website: "I can’t wait to get started here.
“It was always my dream to stay in England, in the Premier League. QPR did well last season to come up and the squad is full of top players, so I’m delighted to be here.
“Harry told me I was a big target for him and when you hear that from a coach, you want to work with them and play for them.
“I’m just looking forward to showing what I’m capable of here at QPR.”
Manager Harry Redknapp praised the acquisition of the 24-year-old, who scored for Netherlands against Chile in the World Cup.
“Leroy’s arrival is a massive boost for us," he stated.
“He’s another excellent signing and I’m delighted we’ve been able to get him to QPR.
“He played for Holland in the World Cup this summer and has all the attributes you'd be looking for from a central midfielder.
“He's just an outstanding midfield player - great physique, fine ability, he gets box-to-box.
“I’m really looking forward to integrating him into the squad.”
Fer could be in line to make his debut at Redknapp's former club Tottenham on Sunday.