His first professional work was a strip called The Crusader in Frantic Magazine for Dez Skinn's revamped Marvel UK line.

[10] In 1985 Davis received his big break in the United States when he was hired by DC Comics to draw Batman and the Outsiders, written by Mike W. Barr.

[11] His work proved popular enough for him to be assigned artistic duties on DC's flagship title Detective Comics in 1986, again with Barr writing.

In 1987 the duo launched the monthly series Excalibur,[15] which featured a team consisting of Captain Britain and Meggan together with former X-Men members Kitty Pryde, Nightcrawler and Rachel Summers.

In 1994 Davis created a new series of original characters called the ClanDestine, which featured the Destines, a family of long-lived, magically powered British superhumans.

[19] During much of the 1990s Davis drew many of Marvel and DC Comics major characters and titles, including JLA: The Nail[20] and The Avengers.

After a return to Uncanny X-Men, working again with Claremont, Davis wrote and drew in 2006–2007 a six-issue Fantastic Four: The End limited series for Marvel[22] (not to be confused with a similar one-shot written by Stan Lee and drawn by John Romita Jr).

In February 2008, Davis wrote and pencilled a five-part ClanDestine miniseries and the one-shot Thor: Truth of History for Marvel.

[23] Davis most recent work has been in Totally Awesome Hulk (#7–8, 2016), the Thanos Trilogy (2018–2019)[24][25] and a reunion with Roy Thomas in 2019 for two issues of The Savage Sword of Conan (#10–11, volume 2).