The England defender has committed to the club until the summer of 2019.
The 25-year old, who has been impressive in a United side in a fine run of form of late, is in his fifth season at the Red Devils and will be hoping to add to the two Premier League titles he's already won in the seasons ahead.
Commenting on the new deal, Smalling said: "I’m delighted to sign my new contract. I am so proud to play for such a great club. 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."
https://twitter.com/ManUtd/status/590515421507416065
Manchester United manager Louis van Gaal added: "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.
"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."
