The Chilean had been with Italian champions Juve for the last two seasons after moving from Serie A rivals Udinese in June 2012.
And, after the 26-year-old's contribution at the World Cup in Brazil, QPR manager Harry Redknapp believes Isla has plenty to offer at Loftus Road.
"He's a top player and we're delighted to have him here," he said. "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 made 51 appearances for his country, added: "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."
Isla follows the likes of Rio Ferdinand, Steven Caulker and Jordon Mutch in making the move to QPR during the close-season.
