"Since I came to United, it's been a whirlwind four years that have passed so quickly. I am very proud to sign my new contract and continue my stay at this great club," Shaw told ManUtd.com.
"I want to thank everybody that has stood by me and shown me huge support - the management, my team-mates and the fans.
"I want to let everyone know that I will give everything I have to repay them and deliver success over the years to come. I'm still very young with a lot more to learn and I can't wait to continue my progress under Jose Mourinho."
Mourinho himself commented, "Luke fully deserves this contract. He understood his development process, he has worked really hard at every level and he always believes in himself which is a great attribute to have.
"Luke is still young and is improving all the time and he must feel very proud of himself. I am delighted that we are keeping such a talented young English player with a bright future ahead of him."