The Portugal international had been linked with an exit from Old Trafford following a disappointing 2012-13 campaign in which he made just seven league starts under then-manager Alex Ferguson.
But new boss David Moyes has signalled his faith in the 26-year-old by handing him a new long-term deal.
"I'm really pleased Nani has re-signed for the next five years," the Scot said.
"He has great ability and experience beyond his 26 years. I've been impressed with his approach to training and look forward to working with him in the coming seasons."
"Playing at United has been a fantastic experience for me," the winger enthused after penning his extension.
"When I came to the club, I never imagined the success we have enjoyed. Training every day with top players who want to win trophies every year is a great motivation to me.
"I'm very happy that the new manager has shown this faith in me and I'm looking forward to helping the team compete for more honours this season."
