Davis began his career in comics drawing the revamped Captain Britain story in The Mighty World Of Marvel. Curiously, as Davis never realized artists drew at a larger size than what was published, his art was drawn as the same size as it would be on publication.
Then, he drew Harry Twenty on the High Rock for 2000AD around six months prior to working with Alan Moore. Davis, Paul Neary, David Thorpe and Moore were responsible for creating D.R. and Quinch for 2000AD. Later Davis replaced Garry Leach on Marvelman in Warrior and yet again worked with Moore.
He drew 14 issues of the monthly Captain Britain title which was later reprinted in trade paperback.
In 1985 Davis was hired by DC Comics to draw their Batman and the Outsiders title, written by Mike W. Barr. His work proved popular enough for him to be assigned artistic duties on Detective Comics, main Batman's series, in 1986, again with Barr writing. During the Batman: Year Two storyline, however, Davis encountered difficulties with his editor and left (his replacement was Todd McFarlane) midway during the storyline.
In 1987 he therefore jumped to Marvel Comics. Here he formed a new creative team with writer Chris Claremont and, after two New Mutants annual and three popular episodes for Uncanny X-Men, the duo launched Excalibur, one of the most amusing US comics of 1980s. The team featured Captain Britain and Meggan together with former X-Men members Kitty Pride, Nightcrwaler and Rachel Summers. The stories, set mainly in England, pivoted mainly on cross-dimensional capers (including several Lewis Carroll's) based on Moore's Captain Britain stories of early 1980s. Davis showed as its best as artist on this series, thanks to effective inks provided by Paul Neary and, later, Mark Farmer.
Davis left with #24, but returned also as writer in #42, showing a passion for creating new, pleasant characters of his own, which included Feron, Cerise, Micromax and Kylun. Davis confirmed this in creating a complete new series of characters maintaining some of the English mythology related Excalibur themes, the unlucky ClanDestine team of 1994. Created for Marvel UK and written and drawn by Davis, it ended with N12 (last four numbers not by Davis) but was briefly revamped by Davis for a cross-over with X-Men. ClanDestine was a Davis creation of his own for Marvel UK, but scored little success in spite of critical praise.
During much of the 1990s Davis drew many of Marvel and DC Comics major characters and titles including JLA: The Nail, The Avengers and Killraven. He was also commissioned to write both main X-Men series in 1999 (providing art for Uncanny X-Men as well), but he left the following year.
In October 2002 he wrote and drew for Marvel a six-issue miniseries revamping a famous comics character of 1970s, Killraven. After a return to X-Men, working again with Claremont, in 2006 Davis wrote and drew Fantastic Four: The End for Marvel Comics.
Recently, Davis drew a 5-issue ClanDestine series and there are three, 38 page ClanDestine related annuals currently in the pipeline, due out in the Summer of 2012. He also did the Avengers Prime mini-series with Brian Bendis, and an issue each of X-Men: Dark Reign and X-Men: Schism jams. He also drew a short run on Captain America and is currently working on a short run of Thor.