Gillen has worked for many years as a video game journalist and has, more recently, worked on various comics. He is perhaps best known for his creator-owned comic Phonogram, created with artist Jamie McKelvie, published by Image Comics. Gillen recently has written numerous projects for Marvel Comics.
Journalism
Gillen has worked for a lengthy list of publications, including PC Gamer UK, The Escapist, Amiga Power (under the pseudonym "C-Monster"), Wired, The Guardian newspaper,Edge, Games Developer, Develop, MCV, Gamesmaster and PC Format, among others.
On the web, Gillen was a founder and major contributor to the PC gaming site Rock, Paper, Shotgun and a games reviewer for Eurogamer.
He is notable for his manifesto www.alwaysblack.com home for New Games Journalism, more simply the model of new journalism applied to videogames journalism.
In 2000, Gillen became the first-ever videogames journalist to receive an award from the Periodical Publishers Association, for New Specialist Consumer Journalist. PPA | PTC New Journalist of the Year Awards
Gillen has also been invited as a guest speaker at games-industry conferences. Animex International Festival of Animation & Computer Games | Speakers
Gillen is a fan of the work of videogame developer Warren Spector writing positive pieces on Spector's games, most notably the Ion Storm produced games Deus Ex and Deadly Shadows. This stemmed largely from Gillen's love of the now-defunct Looking Glass Studios, where Spector also worked.
In September 2010, Gillen declared on the Rock, Paper, Shotgun website that he was leaving full time games journalism to better devote his time to comic-writing and his contract with Marvel.
Comics
Gillen's career also includes the comics he writes both online and in print; he has worked for Warhammer Monthly and Chaos League.
Since 2003, Gillen has collaborated with artist Jamie McKelvie on a comic strip for the official Playstation Magazine UK, entitled Save Point.
His current project, described by Gillen as "my first real comic," Phonogram is another collaboration with McKelvie, the pop-music urban fantasy Phonogram. Veteran comics writer Warren Ellis has dubbed it "one of the few truly essential comics of 2006." The first issue, published by Image Comics, went on sale in August 2006, the first series ran for six issues. The second series run for seven issues, and was launched in December 2008.
On April 14, 2008 it was announced that Gillen would be collaborating with the artist Greg Scott to expand the Warren Ellis's newuniversal mythos with "a story about killing the future" set in 1959 and he wrote Crown of Destruction a Warhammer Fantasy comic. The Phonogram sequel "The Singles Club" started in December 2008, a series of one-shots. He also got more work at Marvel with a Dazzler story and a Beta Ray Bill one-shot and mini-series.
His workload at Marvel increased in late 2009. At HeroesCon it was announced he would be writing a Dark Reign tie-in with the Dark Avengers: Ares mini-series. During the 2009 Chicago Comic Con it was announced that Gillen will collaborate with Steven Sanders on a new ongoing series known as S.W.O.R.D from Marvel Comics. Gillen will also be writing Thor, following J. Michael Straczynski, from issues #604 to 614.
He has also written a series for Avatar Press called The Heat.