Carey was born in Liverpool, England, in 1959 – describing his young self as "one of those ominously quiet kids... [who] lived so much inside my own head I only had vestigial limbs". As a child, he maintained an interest in comics, writing and drawing primitive stories to entertain his younger brother. He studied English at St Peter's College, Oxford, before becoming a teacher. He continued to teach for 15 years before moving on to writing comics.
After a series of one-off jobs for independent comics companies, including a biographical comic of Ozzy Osbourne and a fantasy about the band Pantera, Carey gained regular employment at 2000 AD, where he created the original series Th1rt3en and Carver Hale.
For the Vertigo imprint of DC Comics Carey went on to write the entire run of the Eisner Award-nominated comic book Lucifer, and issues 175 to 215 of Hellblazer, a run on that title only exceeded in length by Garth Ennis and Peter Milligan. He also wrote the original graphic novels The Sandman Presents: The Furies with John Bolton and Hellblazer: All His Engines with Leonardo Manco.
He is the ongoing writer of X-Men: Legacy working with artist Scot Eaton, plus Ultimate Fantastic Four for Marvel Comics.
He also had three recent Vertigo series that have wrapped up: Faker a six-part mini-series with art by Jock; a second graphic novel, God Save the Queen, with John Bolton, featuring Queen Titania, Oberon, Puck, Nuala and Cluracan from the Sandman and Books of Magic comics; and Crossing Midnight with Jim Fern. September 2006 saw the long-delayed debut of Wetworks: Worldstorm with Whilce Portacio for Wildstorm Comics. He is also one of the first authors on DC's Minx imprint for teenaged girls, his second Minx title being co-written with his daughter, Louise. The Unwritten premiered in May 2009, with art by Peter Gross and covers by Yuko Shimizu.
In 2008 Carey worked on a number of different titles, including tie-ins to the "Secret Invasion" crossover storyline, that included an eight-page story in the one-shot anthology Secret Invasion: Who Do You Trust?, which features Abigail Brand of S.W.O.R.D., and a four-issue mini-series, Secret Invasion: X-Men. That same year he began writing Queen's Rook, the first of Virgin Comics' Coalition Comix on MySpace, where users could suggest ideas for a comic which would then get made. He also wrote "Dark Deception", a crossover story arc that appeared across X-Men: Legacy and Wolverine: Origins, and tied into X-Men: Original Sin, he retold the Beast's origin story in X-Men: Origins, wrote an Iceman story in X-Men: Manifest Destiny, a comic book adaptation of Ender's Shadow, and the Vertigo Comics series The Unwritten.
Carey's first prose novel, The Devil You Know, was released in the UK by Orbit books in April 2006, and as a hardcover in the US in July 2007. Its sequel, Vicious Circle, was published in October 2006, and the following three novels in the series, Dead Men's Boots, Thicker Than Water, and The Naming of the Beasts, followed in September 2007, March 2009 and September 2009, respectively.
Carey's first feature film, the erotic ghost story Frost Flowers, was reported in June 2006 to be in pre-production, with filming to begin that September under the direction of Andrea Vecchiato, but the project collapsed before production began and the script is in limbo. Carey is also working on the TV series The Stranded, the first co-production between Virgin Comics and the Syfy network.
In 2011 he wrote a crossover between X-Men Legacy and New Mutants titled Age of X. In August 2011, Marvel announced Mike Carey's final X-Men-Legacy arc.
In January 2014, he had another prose novel published which was titled The Girl With All The Gifts. It was released to critical acclaim and was later that year announced to be made into a film. Filming began in May 2015, with newcomer Sennia Nanua in the lead role of Melanie, Gemma Arterton as Helen Justineau, Glenn Close as Caroline Caldwell, and Paddy Considine as Sergeant Parks. TV veteran Colm McCarthy directed the movie.