Earlier in his career Collins worked for Marvel UK on Spider-Man, Spider-Man and Zoids, Transformers, Captain Britain, The Real Ghostbusters, Thundercats, Action Force and Doctor Who. As a writer, he created the characters Assassin-8 and Thunderclap in Spider-Man, and wrote the Cherubim and two instalments of Captain Britain. For three years, he was the principal artist on the Judge Dredd Newspaper Strip. Since the late 1980s, he has worked extensively in American comics, primarily for DC (though he was also, notably, the first artist to draw Gambit of the X-Men for Marvel). He has drawn numerous TV and movie tie-in comics, including Star Trek and Babylon 5.
Collins currently does illustrations and comic strips for the Doctor Who Magazine, has illustrated two graphic novels about Daleks, has contributed art to the Harry Potter trading card game, and wrote and designed the first ever Welsh language graphic novel.