The versatile Isla, who plays mainly as a right wing-back, impressed for Chile at the World Cup, but he had fallen well down the pecking order at Juventus and struggled to hold down a regular place in the side last season.
The 26-year-old had attracted the interest of a number of clubs but Rangers won the race for his signature.
QPR manager Harry Redknapp told his club’s official website: “He’s a top player and we’re delighted to have him here.
“He showed his quality in the World Cup for Chile and it’s a great loan signing for us.
“He’s a versatile player, he’s full of energy. I’m confident he’ll be a really big asset for us this season”
Isla, who has 51 Chile caps, said: “I am very happy to be here. This is the start of an exciting new adventure for me.
“Everybody knows that the Premier League is the greatest league in the world and the QPR proposal is very interesting and one I am very excited about.
“I hope this coming season is going to be great for both the club and myself. I will give 100 per-cent in every game to help QPR in the Premier League.”