Smith was born in Kansas City, Missouri, but only lived there three days. His father was a U.S. Naval aviator, and the family moved several times during his childhood. As a young comics fan, Smith particularly admired the work of Steve Ditko on The Amazing Spider-Man and Neal Adams on Batman.
Smith had no formal art training aside from some course in airbrushing. Before becoming a professional comic book artist, Smith worked as an animator. In 1977, he began work on the animated adaptation of The Lord of the Rings produced and directed by Ralph Bakshi. He also worked on Bakshi's film American Pop.
He first came to attention at Marvel Comics in the early 1980s, where he filled in on a variety of Marvel titles, including Marvel Fanfare #4, cover dated September 1982, doing the final chapter of an X-Men story, and Doctor Strange #56, cover dated December 1982, pencilling a re-telling of his origin. The following month began his run on Uncanny X-Men, then the biggest selling US comic. He drew the X-Men from #165 - #175 (with the exception of #171), replacing Dave Cockrum. A few months after leaving the X-Men, he returned as the regular artist on Doctor Strange. He worked on that series from #65 - #73, drawing 7 of those issues. Smith's brief run on X-Men left a large impact, and most of it was later reprinted in the From The Ashes trade paperback. Eventually his entire X-Men run was reprinted in Essential X-Men Vol. 4. He bookended the Marvel Fanfare series, pencilling a short Daredevil story in issue #1, and writing, drawing and lettering a sequel to that Daredevil tale in #60, the final issue of the book. Smith would briefly revisit the X-Men, drawing the X-Men / Alpha Flight limited series as well as a brief stint on the X-Men spin-off X-Factor. Since the mid-1980s Smith has worked as an artist on a range of comics titles, including work for the X-Men stable.
Perhaps his best-known work outside of the X-Men are The Golden Age and the young adults comic Leave It to Chance, both collaborations with writer James Robinson. Smith has also contributed art to a number of First Comics titles including American Flagg!, Nexus, and GrimJack.
Among Smith's most recent work is the Kitty Pryde: Shadow and Flame limited series written by Akira Yoshida.