United had a clause in Valencia's contract, which they have triggered to keep the 31-year-old until at least June 2018, as announced by the club on their official website on Tuesday.
The Ecuador international was brought to Old Trafford by Sir Alex Ferguson from Wigan Athletic in 2009. He was the club's first signing after the departure of Cristiano Ronaldo to Real Madrid, as noted by BBC Sport.
A consistent performer with great strength and technical ability, Valencia has become a mainstay across the wide areas for United.
The news was also announced on the club's Twitter account:
His agility has particularly shone through in his role as an attacking full-back, and he is a firm favourite among United supporters.
Per United, Valencia was named Fans' Player of the Year and Players' Player of the Year in the 2011-12 season.
Red Devils manager Jose Mourinho is likely to have been boosted by the reliability of Valencia's displays this season.
While the Portuguese has shown a tendency to shuffle personnel in defensive areas, Valencia has featured more regularly than most, including 18 times in the Premier League.
His all-round game arguably offers Mourinho far greater options. His crossing and talent for getting to the byline, allied to a smart, hardworking defensive ethic are no doubt a boon for any manager.
The decision to extend his deal looks likely to mean Valencia will see out a stellar career at United.