While still following art studies, Sean Philllips began working for the British Fleetway agency, illustrating stories with 'Judge Dredd' for 2000AD. At the beginning of the 1990s, he went to work for the US market, where he started out working extesively on DC/Vertigo's 'Hellblazer' title. For the Vertigo imprint, Phillips has also illustrated some issues of Peter Milligan's 'Shade, the Changing Man', the regular 'Kid Eternity' series, as well as the graphic novels 'The Heart of the Beast' (co-written by Dean Motter) and the Peter Milligan scripted 'Vertigo Verité: Hell Eternal' and 'The Minx'. In 2001, he cooperated with fellow artist John Bolton on the miniseries 'User'.
While working for Vertigo, Phillips also cooperated on more commercial titles, such as 'Batman' and its fellow titles 'Legends of the Dark Knight', 'Gotham Knights' and, most notably, 'Gotham Noir'. The latter was scripted by Ed Brubaker, with whom Phillips began the 'Sleeper' title at DC/Wildstorm in 2003. He also cooperated on Marvel's 'Webspinners: Tales of Spider-Man', 'X-Patrol' and 'Wildcats'. With Bruce Jones, he created the maffia title 'Kingpin'. With Ed Brubaker, he has worked on 'Criminal' for Icon Comics.