Dillon got his first professional work at the age of 16, drawing the title story in the first issue of Hulk Weekly for Marvel UK, later working on the Nick Fury strip. In the 1980s he also drew for Warrior and Doctor Who Magazine, where he created the character of Abslom Daak. He did a considerable amount of work for the comics 2000 AD and Warrior.
Along with Brett Ewins, Dillon started the comic magazine Deadline in 1988, which continued for another seven years.
Together with author Garth Ennis, Dillon worked on Hellblazer and, later, on the very successful (and critically acclaimed) Preacher which wrapped up in 2000 after 66 issues. Dillon also created the character Dogwelder, featured in Ennis's series Hitman.
Recently, Dillon has done mostly work for Marvel Comics, pencilling for the relaunched Punisher series and new miniseries (also with Ennis), Supreme Power: Nighthawk, and Wolverine: Origins.
As of July 2007 he has successfully sold Preacher to Hollywood for the film/TV series production, although no confirmation on its actual takeup is yet guaranteed.
It is often said he dislikes fame, however he admits to enjoying the trappings of success!