The former England manager had been out of the game since he quit FC Twente in February after a disappointing second spell in charge.
He had hoped to return in a managerial capacity but was pipped to the vacant Wigan post by ex-Bolton boss Owen Coyle.
McClaren will now try to help another relegated club back to the Premier League at the first attempt, working alongside Kevin Bond, Joe Jordan and Steve Cotterill as part of manager Harry Redknapp's backroom staff.
"I am delighted to have been able to bring Steve in," Redknapp told QPR's official website.
"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.
"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."
McClaren said: "I'm delighted to take up this position offered to me by Harry and QPR.
"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."
McClaren had enjoyed a rising reputation in the game after a successful spell as assistant manager under Sir Alex Ferguson led to him being appointed as Middlesbrough boss.
He took the club to League Cup success and a UEFA Cup final before an ill-fated spell as England manager ended acrimoniously after a 3-2 defeat to Croatia saw England miss out on a spot at Euro 2008.
With that disappointment fresh in his mind McClaren ventured abroad and rebuilt his career by delivering the Eredivisie title to Twente.
He left for Wolfsburg but was largely unsuccessful, as was the case during a short stint at Nottingham Forest, before he moved back to Twente.
He could not replicate his earlier successes with the Enschede club, however, and resigned earlier this year.