McNeill was born in Glasgow, Scotland and studied architecture and then building surveying at the and Glasgow Caledonian University from 1989—1996. In 1996 he started work in an architects’ office designing new flats and commercial properties, until he saw an advertisement for a writer in the December 1999 copy of White Dwarf.
In February 2000, Graham started work for Games Workshop as a staff writer for games development, writing articles for White Dwarf and army-specific books. In May 2000 he started writing for the Warhammer 40,000 team, but has also kept up writing articles for White Dwarf. Graham has been heavily involved working on codex, especially Warhammer 40,000 Codex: Tau (Chambers et al., 2001) between late 2000 and June 2001. Other codexes he has been involved with are Warhammer 40,000 Codex: Necrons (Chambers et al., 2002), Warhammer 40,000 Codex: Chaos Space Marines (Games Workshop Design Staff, 2002), Warhammer 40,000 Codex: Imperial Guard (Chambers et al., 2003) and Warhammer 40,000 Codex: Daemonhunters (McNeill and Haines, 2003). Since a promotion from staff writer to games developer, he has written Warhammer 40,000 Codex: Witch Hunters (McNeill et al., 2003) and Warhammer 40,000 Codex: Space Marines (Chambers, 2004).
Graham is an avid writer and has had several novels published by The Black Library. They are Nightbringer (McNeill, 2005) published in January 2002, Storm of Iron (McNeill, 2003) in July 2002, Warriors of Ultramar (McNeill, 2004a) in February 2003 and Dead Sky Black Sun (McNeill, 2004). In addition McNeill has written The Ambassador, a Warhammer novel, in November 2003, "The Ambassador Chronicles" in July 2005, "Guardians of the Forest" in September 2005.His most recent works have been False Gods (McNeill, 2006), published in June 2006, Fulgrim (McNeill, 2007), published in July 2007,and Mechanicum (McNeill, 2008), the three of which are part of the Black Library's Horus Heresy novel series. Another part to McNeill's story about the Ultramarines, The Killing Ground, was released in May 2008.
In April 2009, Graham also contributed to the anthology book Tales of Heresy with a story entitled The Last Church, one of the first stories in the Black Library imprint in which the Emperor spoke directly and at length, rather than described from afar as had so far been the case in the Horus Heresy series. Early in 2010, Graham then released A Thousand Sons, a Horus Heresy novel focusing on the Thousand Sons legion and their fall from the graces of the Emperor by the hand of the Space Wolves. This novel was written in sync with a novel due to be released in early 2011 by Dan Abnett, titled Prospero Burns, which tells the same narrative from the opposite perspective.
Graham worked closely with Abnett on the two novels, ensuring they met at certain points and would not contradict one another. This planning was rewarded when, a month after A Thousand Sons was published, it not only reached the top of the UK science fiction charts (displacing a long-held spot by the novels of Charlaine Harris), but soon entered at number 22 on the New York Times Bestseller List, cementing his reputation as a writer of high-standard tie-in fiction.
Graham plays both Warhammer 40,000, in which he plays with both Tau and Necron armies, he started with The Ultramarines, and Warhammer, in which he plays an Empire army.
