The former South Korea international has signed a two-year deal with Mark Hughes' side who, as Goal.com reported, have paid in the region of £2.5 million for the 31-year-old and will also part with a further £2.5m should they avoid relegation next season.
Park moves to Loftus Road after spending seven trophy-laden years at Old Trafford, and admitted the offer from QPR was too good to turn down.
"QPR is a club with huge history and tradition, and a great ambition to achieve at the very highest level," he told the club's official website.
"I am joining a club that is very much on an upwards curve - a club that has a very bright future"
"I am joining a club that is very much on an upwards curve - a club that has a very bright future. The infrastructure is in place, with a new training ground and plans for a new stadium, for us to achieve in the short and long term.
"The manager has a proven track record at Premier League level and I am looking forward to working with him and the rest of the squad to help take this club to the next level."
QPR boss Hughes also described Park as a "huge signing" for the club and believes that the midfielder's experience in high-profile matches will have a big impact next term.
"We are delighted Ji is going to join us because his record speaks for itself. He has been a big player for Manchester United and played a big part in their success in recent years," said the manager, himself a former Red Devils player.
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"He was always picked for the big matches because they could rely on him, and we are going to reap all those qualities.
"I think it is fair to say Ji has been attracted not by where QPR are, but where QPR are going. We were able to show him where we feel the club is heading and he embraced it.
"He felt this was a good option for him and after giving seven great years to United he wanted a new challenge. He sees QPR as very much a club on the up and wants to be part of something that is going to be very special."