In the original Star Wars: Episode IV A New Hope, Harris portrayed Leia's Rebel Escort, as well as a Rebel mechanic in the war room in a separate scene. Harris also portrayed a Stormtrooper.
In The Empire Strikes Back, Harris was cast as Merril and later Bossk. Harris also played a Rebel on Hoth who is told to "prepare for ground assault" by Carlist Rieekan as well as a Stormtrooper on Cloud City.
Harris' only onscreen appearance in Return of the Jedi was portraying a Stormtrooper again.
Harris doubled for Anthony Daniels inside the C-3PO costume from The Empire Strikes Back onto Return of the Jedi. The Boba Fett costume was made around him; various photos from the costume test exist. Harris later donned the Boba Fett costume while doubling for Jeremy Bulloch on the set for Return of the Jedi, leading to a mixup with fellow costumed actor Trevor Butterfield who was portraying Harris' former character Bossk. Harris' body was molded for the carbonite block of Han Solo. Due to C-3PO and Bossk occupying the same scenes during Return of the Jedi, the role of Bossk was handed off to Trevor Butterfield while Harris stood in for Daniels' for lighting.
On short notice, Harris returned to the saga to double as Terence Stamp in The Phantom Menace due to Harris' resemblance to the actor.
Following his death in 2020, the first issue of the comic book series Star Wars: Bounty Hunters was dedicated to him.