"I am feeling good, enjoying my football more than ever and, most importantly, I feel I am making a contribution to the team," said the 39 year old.
"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 boss Sir Alex Ferguson said: "Ryan is an example to us all, the way in which he has, and continues to, look after himself.
"What can I say about Ryan that hasn't already been said? He is a marvellous player and an exceptional human being.
"He has fantastic energy for the game and it is wonderful to see. Ryan seems to reach a new milestone every week, and to think that he now has 23 unbroken years of league goals behind him is truly amazing in the modern-day game. I don't think it will ever be achieved again by anyone.
"His form this year shows his ability and his enjoyment of the game are as strong as ever and I am absolutely delighted that he has signed a new contract."
"The plan is for Ryan to stay on (at the club after he's finished playing)," added Ferguson. "Involvement after they've played here is important, whether that be as a coach or assistant manager or working with the youth team.
"If anyone has ambitions to be a manager you should take on different roles before you get there, almost as a preparation. He [Giggs] has got to take his badges and spend time with the young players in the academy and prepare eventually to be a manager."