Abnett read English and matriculated at St Edmund Hall, Oxford in 1984, and graduated from there in 1987. He attended some subjects with Stewart Lee.
As one of the more prolific 2000 AD writers, Abnett was responsible for the creation of one of the comic's better known, and longest-running, strips of the last decade, Sinister Dexter. Other original stories include Black Light, Badlands, Atavar, Downlode Tales, Sancho Panzer, Roadkill, Wardog based on the game of the same name, Kingdom and Brink. Abnett has also contributed to some of the comic's major ongoing series, including Judge Dredd, Durham Red and Rogue Trooper.
His work for Marvel includes runs on Death's Head 2, Battletide, Knights of Pendragon (all of which he co-created), The Punisher, War Machine, Annihilation: Nova and various X-Men titles, as well as several stories for the Doctor Who Magazine comic strip.
At DC he is probably best known for his 2000 relaunch of Legion of Super-Heroes as the limited series Legion Lost and then the ongoing series The Legion. His work for DC is usually co-written with Andy Lanning and they are often referred to as DnA. The two co-created the Resurrection Man character with artist Jackson Guice in 1997.
For Dark Horse Comics he co-wrote Planet of the Apes: Blood Lines with Ian Edginton, as well a penning Lords of Misrule and HyperSonic.
Abnett's First & Only was one of the first novels published by Games Workshop's Black Library. His other novels set in Games Workshop's Military science fiction-themed Warhammer 40,000 universe include the Gaunt's Ghosts series, the Eisenhorn and Ravenor trilogies, and more recently, as part of the Horus Heresy series, the SF best-sellers Horus Rising, Legion, Prospero Burns and Know No Fear. He has also authored four comic strip series, later collected as graphic novels, for Games Workshop's Black Library imprint: Damnation Crusade, Lone Wolves, Inquisitor Ascendant and Titan.
Having written two Doctor Who audio dramas – The Harvest and Nocturne – for Big Finish's series, as well as Torchwood: Everyone Says Hello for BBC Audio, Dan was also the author of two novels based on the BBC's revived science-fiction series: The Story of Martha and Torchwood: Border Princes.
In 1994, he wrote a promotional comic to promote the opening of the Nemesis roller coaster at Alton Towers.
At 2000 AD he finished the final book of The V.C.s and started Black Atlantic in the Judge Dredd Megazine, which was drawn by Steve Roberts (seen working on Bec & Kawl) in black and white.
In 2008 Abnett and Lanning took over The Authority as part of the World's End relaunch of the core Wildstorm titles.
In addition, Abnett has done a lot of work on Marvel's "cosmic" characters. They expanded on their work in Annihilation: Nova and Nova, and piloted the next big event Annihilation: Conquest. They said "we were approached by Andy Schmidt, who edited the first 'Annihilation' event, and asked to pilot the next event, which Bill Rosemann is editing." They ended up writing the Prologue, the Nova series crossover and the main Annihilation: Conquest limited series. The characters then became the core of a new Guardians of the Galaxy.
In June 2008, Abnett and Lanning signed an exclusive deal with Marvel, which they hoped would give them time to work on the "cosmic" characters they have been dealing with, as well as more earth-based ones. The contract allowed them to finish existing commitments, so they will be able to finish their fifteen issue run on The Authority. In addition Marvel has allowed the contract to include "a couple of exceptions that are not direct competition, for example, Dan's 2000AD work in the UK and his Games Workshop novels." The first major work to emerge after this deal will be War of Kings, a crossover storyline, emerging from Secret Invasion, that pitches Black Bolt (and the Inhumans) against Gabriel Summers (and the Shi’ar Empire) but also draws in other teams and characters, including Nova, the Guardians of the Galaxy and the Starjammers. This then led straight into "Realm of Kings" which deals with how the different groups deal with the fallout from the events in War of Kings and this, in turn, was followed by The Thanos Imperative. DnA have also written an Iron Man/Thor limited series.
He and Lanning have also written Fusion, a crossover series between Marvel and Top Cow.
He also started Insurrection, a series in Judge Dredd Megazine that aimed "to bring to the Dredd Universe something of the epic war-in-space scale of the stuff I write for Warhammer 40K."
Abnett wrote the screenplay for Games Workshop and Codex Pictures's CGI film Ultramarines released in 2010.
Abnett concluded Insurrection and began a new series in the same milieu, also in the Judge Dredd Megazine. Meanwhile, in 2000AD he has continued Kingdom, contributed Grey Area and began another new series, Brink.
On 19 March 2009, HarperCollins' science fiction, fantasy and horror imprint, Angry Robot, announced the acquisition of three original fiction titles by Abnett. The press release from Angry Robot announced: