The 30-year-old, who had a year to run on his existing deal, has extended his stay at Old Trafford until summer 2013.
"I have enjoyed every minute of my time at United," the club's website quotes Park as saying. "I’m delighted to be part of the club during this latest stage in its history, with another exciting young team being built.
"I’m looking forward to playing my part in keeping United at the top of the game."
Red Devils boss Alex Ferguson added: “Ji has been an important player for us for a number of years now. He has great ability and energy and in recent seasons has added the knack of scoring important goals in big games."
The former South Korea international has scored 24 goals in 177 appearances since joining the club from PSV Eindhoven in 2005.