The 52-year-old, who has been out of work since leaving FC Twente in February, has been praised by R's boss Harry Redknapp.
"I am delighted to have been able to bring Steve in. Everyone in the game knows what a top coach he is and he'll add something different to the group, regardless of how long he is with us for," Redknapp told the club's official website.
"This is a very important season for us and I wanted to look at freshening up the whole place, not just the playing side. I want new ideas, different opinions and another experienced head to speak to. That's what Steve brings.
"Along with Kevin [Bond] and Joe [Jordan], I've got a brilliant backroom team and their input is going to be so important for me this season. Steve adds to the excellent staff I already have here."
McClaren himself said that he is "delighted" to join QPR and is determined to help them regain their Premier League status.
"I'm delighted to take up this position offered to me by Harry and QPR," he said. "Whilst it still remains my ambition to manage again, this gives me an ideal opportunity to stay involved and work on the field with one of the top managers in this country and a very ambitious club.
"Rest assured, I'll be doing all I can for Harry, the club and the fans to help QPR return to the Premier League."
QPR were relegated from the Premier League last season.