The midfielder, who will turn 40 later this year, has decided to prolong his career with the former Premier League champions on the eve of his 1,000th senior appearance for the North-West outfit.
"I am feeling good, enjoying my football more than ever and, most importantly, I feel I am making a contribution to the team," Giggs told the club's official website. "This is an exciting team to be part of, with great team spirit, and we are again pushing for trophies as we head towards the business end of the season."
United manager Sir Alex Ferguson added: "What can I say about Ryan that hasn't already been said? He is a marvellous player and an exceptional human being. Ryan is an example to us all, the way in which he has, and continues to, look after himself."
The former Wales international is expected to reach his 1,000th-game milestone in tomorrow's league fixture against Norwich City.