The South Korea international, 31, has joined the London club for an undisclosed fee.
Park is manager Mark Hughes' sixth summer capture, joining Ryan Nelsen, Andy Johnson, Rob Green, Samba Diakite and former Old Trafford team-mate Fabio at Loftus Road.
The ambitious club also claim his signing will "put the QPR brand on a global scale", heading up their attempts to break into the Asian market.
Rangers, promoted in 2011, only escaped relegation from the Premier League on the final day of last season and are determined to avoid a similar struggle next term.
Park leaves United after seven years, during which time he made 203 appearances and scored 27 goals, winning four Premier League titles and the Champions League in 2008.
Hughes said: "On a football level, Ji is someone I have admired from afar for years.
"He wore the red shirt of Manchester United in a distinguished way and he will bring a great deal to the team, I can't wait to start working with him.
"Ji is a motivated guy, he feels there is success ahead of him, he ticks every box. It's a very exciting time for QPR.
"I said at the end of the season we didn't want to be in the same position next season and I stand by that, we are in a better place now."
Park, who arrived in England from PSV Eindhoven in 2005, added: "I know QPR want to improve and have ambitions to reach the next level and I will try my best to help.
"There were other offers but nothing compared to QPR."
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