John appeared in A Bridge Too Far (1977), in the 1980 hit sequel film Superman II as an astronaut named Nate, also that year he appeared in Flash Gordon. He was featured in the BBC television series Oppenheimer (1980). He portrayed Dak Ralter, Luke Skywalker's Gunner during the Battle of Hoth in The Empire Strikes Back. When Jeremy Bulloch played an Imperial Officer, he needed someone to cover him as Fett. Morton being similar in height was a body double for two days in costume. He filmed with another unit, the sequence when Fett confronts Darth Vader in the Bespin hallway during Han Solo's torture - while Bulloch filmed his scenes as the Imperial Officer. Afterwards he left Hollywood and eventually settled in public relations work back in Annapolis.
He is also an accomplished musician (guitar player) and a writer (Backstory in Blue, 2008).