The 19-year-old Northern Irishman has broken into the United first-team squad under manager Louis van Gaal and has made 12 appearances to date this season, playing in central defence and at right-back.
“Paddy has risen through the ranks to become an integral part of the first-team squad. He has all the attributes to develop into a top player,” Van Gaal said in a statement on the United website.
“Promoting youth players is very important both to myself and to the club and I am delighted Paddy has signed a new contract.”
Follow us at our new home on Twitter @NatSportUAE