He then worked as a freelance illustrator for advertising from 1983 when he met
John Higgins who was writing a music magazine comic story, The Bizniz. Sullivan ended up colouring
Steve Yeowell's art on the story and later Higgins introduced him to the editors at
Marvel UK.[1] He began work there in 1987 providing covers for The Transformers[2] until he got his break in 1988 drawing a Doctor Who story written by
John Freeman.[3] and has subsequently been published in a number of titles including: Transformers, ThunderCats, Death's Head, RoboCop, TekWorld, Thunderbirds (from 2000 to 2005)[4] and 2000 AD.
He has worked on various
Doctor Who strips, contributing semi regularly to Doctor Who Magazine since 1988, drawing the
Eighth Doctor strips that appeared in the Radio Times in 1996 and drawing 64 strips for Doctor Who - Battles in Time from 2006 to 2009. He has also provided artwork for Doctor Who webcasts that appeared on
BBCi including Death Comes to Time, Real Time and Shada along with artwork for the official Doctor Who website. He produced line artwork for alternate issues of Doctor Who DVD Files and worked as pencils/inks artist on The Amulet of Samarkand graphic novel for
Hyperion Books which was published in late 2010. In 2013 Sullivan returned to Doctor Who comic strips this time for the US
IDW producing artwork for the Second Doctor instalment of their 50th Anniversary story 'Prisoners of Time', and also an
Eleventh Doctor strip used in the
Royal Mail Doctor Who Prestige Stamp Book, part of the range of UK commemorative stamps issue. 2014 saw the release of Titan's
Twelfth Doctor comic book series and Sullivan created a variant cover for issue 1. A frame he drew from the 1989 DWM
Seventh Doctor comic strip 'Nemesis of the Daleks' featuring
Abslom Daak appears briefly in the 2014 televised
Doctor Who episode Time Heist.
From 2015 to 2018 he was regular artist on Titan Comics '
Rivers of London' comic - a canonical comic strip extension of the series of novels written by
Ben Aaronovitch concerning the supernatural police procedural fantasy adventures featuring full-time policeman and trainee wizard Peter Grant. The comic book series was written by
Doctor Who alumni Aaronovitch and
Andrew Cartmel. Since leaving the series, Sullivan has produced graphic novels for Penguin publishing and from 2022 - 2024 was regular artist for Doctor Who Magazine - featuring the first Fourteenth Doctor story (canonical according to showrunner Russell T Davies) and the Fifteenth Doctor's first ever comic strip story.
Sullivan plays the saxophone and toured the UK as part of a
Roxy Music tribute band for over a decade before quitting in 2015.