The England international defender, 25, has won two Premier League medals with the Red Devils since joining them from Fulham five years ago.
In total he has made 147 appearances and scored nine goals, four of them in the current campaign, since his debut against Chelsea in the Community Shield in August 2010.
"Chris has developed immensely during the short time that I have been at the club and has become an integral part of the first-team squad"
Louis van Gaal
United boss Louis van Gaal is delighted to have secured the future of one of the "integral" members of his side.
"Chris has improved and developed immensely during the short time that I have been at the club and has become an integral part of the first-team squad," said the Dutchman.
"He always conducts himself in a very professional manner and it is also pleasing that he has scored some important goals this season too. I am delighted he has signed a new contract."
Smalling himself is naturally pleased to be extending his stay, and he is looking forward to an exciting future.
"I'm delighted to sign my new contract. I am so proud to play for such a great club," said the former Maidstone centre-half.
"We have developed as a team over the course of the season under Louis van Gaal and we are now playing as a complete unit.
"This is a very exciting time to be at Manchester United, we are all determined to get back to where we belong and competing at the highest level."
