Moore started out writing for British underground and alternative fanzines in the late 1970s before achieving success publishing comic strips in such magazines as 2000AD and Warrior. He was subsequently picked up by the American DC Comics, and being "the first comics writer living in Britain to do prominent work in America",(p7) he worked on some of their big name characters such as Batman, Superman and Swamp Thing, penning titles like Watchmen, The Killing Joke and Whatever Happened to the Man of Tomorrow?. During that decade, Moore would be one of the comic book novelists that helped to bring about greater social respectability for the medium in the United States and United Kingdom,(p11) and has subsequently been attributed with causing the development of the term "graphic novel" over "comic book". In the late 1980s and early 1990s he left the comic industry mainstream and went independent for a while, working on experimental work such as the epic From Hell, pornographic Lost Girls and a non-comic novel, Voice of the Fire. He subsequently returned to the mainstream later in the 1990s, working for Image comics, before gaining control of his own personal imprint, America's Best Comics, through which he published works like The League of Extraordinary Gentlemen and the occult-based Promethea.

A countercultural figure, Moore is also known as a Neopagan, occultist and ceremonial magician, and has featured such themes in works like Promethea and From Hell as well as performing avant-garde spoken word occult "workings" with The Moon and Serpent Grand Egyptian Theatre of Marvels, some of which have been released on CD.

Despite his own personal objection to such projects, his books have provided the basis for a number of Hollywood films, including From Hell (2001), The League of Extraordinary Gentlemen (2003), V for Vendetta (2005) and Watchmen (2009). Alongside this, Moore has also been referenced in various aspects of popular culture and has been recognised as an influence on a variety of literary and television figures including Neil Gaiman, Joss Whedon and Damon Lindelof.

Moore was born on 18 November 1953, at St. Edmond’s Hospital in Northampton, England, to a working class family who he believed had lived in the town for several generations.(p11) He subsequently grew up in a part of Northampton known as The Burroughs, a poverty-stricken area with a lack of facilities and high levels of illiteracy, but he nonetheless "loved it. I loved the people. I loved the community and… I didn’t know that there was anything else."(pp13-16) He lived in his house with his parents, brewery worker Ernest Moore and printer Sylvia Doreen, along with his younger brother Mike and his maternal grandmother.(p14) He "read omnivorously" from the age of five, getting books out of the local library, and subsequently attended Spring Lane Primary School.(p17) At the same time, he began reading comic strips, initially those which were British in origin such as Topper and Beezer, but eventually obtaining some American imports such as Flash, Detective Comics, Fantastic Four and Blackhawk.(p31) He later passed his eleven plus exam, and was therefore eligible to go to Northampton Grammar School, where he first came into contact with people who were middle class and better educated, and he was shocked at how he went from being one of the top pupils at his primary school to one of the lowest in the class at secondary. Subsequently disliking school and having "no interest in academic study", he believed that there was a "covert curriculum" being taught that was designed to indoctrinate children with "punctuality, obedience and the acceptance of monotony."(pp17-18)

"LSD was an incredible experience. Not that I’m recommending it for anybody else; but for me it kind of - it hammered home to me that reality was not a fixed thing. That the reality that we saw about us every day was one reality, and a valid one - but that there were others, different perspectives where different things have meaning that were just as valid. That had a profound effect on me."

Meanwhile, in the late 1960s, he became interested in the Hippie movement, at the time believing in its ideals that everyone would be "brothers in the Age of Aquarius."(p18) He also began publishing his own poetry and essays in fanzines, and eventually helped to set up his own fanzine, titled Embryo, and through this got involved in a Hippy group known as the Arts Lab, which the magazine fused with.(pp33-34) Influenced by the writings of Timothy Leary, he began dealing LSD at school, being expelled for doing so in 1970 - he later described himself as "one of the world's most inept LSD dealers". The headmaster of the school subsequently "got in touch with various other academic establishments that I'd applied to and told them not to accept me because I was a danger to the moral well-being of the rest of the students there. Which was possibly true."(p18)

Whilst continuing to live in his parents' home for a few more years, he moved through various jobs, including cleaning toilets and working in a tannery. Around 1971, he met and began a relationship with a Northampton-born girl named Phyllis, with whom he moved into "a little one-room flat in the Barrock Road area in Northampton." Soon marrying, they moved into a new council estate in the town's eastern district whilst he worked in an office for a sub-contractor of the local gas board. However, he felt that he was not being fulfilled by this job, and so decided to try and earn a living doing something more artistic.(pp34-35)

Abandoning his office job, he decided to instead take up both writing and illustrating his own comics. He had already produced a couple of strips for several alternative fanzines and magazines, such as Anon E. Mouse for the local paper Anon and St. Pancras Panda, a parody of Paddington Bear, for the Oxford-based Back Street Bugle.(pp16-17) His first paid work was for a few drawings that were printed in NME music magazine, and not long after he succeeded in getting a series about a private detective known as Roscoe Moscow published using the pseudonym of Curt Vile (a pun on the name of composer Kurt Weill) in the weekly music magazine Sounds, earning £35 a week. Alongside this, he and Phyllis, along with their newly born daughter Leah, began claiming unemployment benefit to supplement this income.(p36) Not long after this, in 1979 he also began publishing a new comic strip known as Maxwell the Magic Cat in The Northampton Post, under the pseudonym of Jill de Ray (a pun on the Mediaeval child murderer Gilles de Rais, something he found to be a "sardonic joke"). Earning a further £10 a week from this, he decided to sign off of social security, and would continue writing Maxwell the Magic Cat until 1986.(pp36-37) Moore has stated that he would have been happy to continue Maxwell's adventures almost indefinitely, but ended the strip after the newspaper ran a negative editorial on the place of homosexuals in the community. Meanwhile, Moore decided to focus more fully on writing comics rather than both writing and drawing them, stating that "After I'd been doing [it] for a couple of years, I realised that I would never be able to draw well enough and/or quickly enough to actually make any kind of decent living as an artist."(p15)

In order to learn more about how to write a successful comic book script, he asked advice from his friend, the comic book writer Steve Moore, whom he had known since he was fourteen.(p20) Interested in writing for 2000AD, one of Britain's most prominent comic magazines, Moore then submitted a script for their long running and successful series Judge Dredd. Whilst having no need for another writer on Judge Dredd, which was already being written by John Wagner, 2000AD's editor Alan Grant saw promise in Moore's work - later remarking that "this guy's a really fucking good writer" - and instead asked him to write some short stories for the series Future Shocks instead. Whilst the first few were rejected, Grant gave Moore advice in improvements, and eventually accepted one of them, which would prove to be the first of many. Meanwhile, Moore had also begun writing minor stories for Doctor Who Weekly, and later commented that "I really, really wanted a regular strip. I didn’t want to do short stories… But that wasn't what was being offered. I was being offered short four or five page stories where everything had to be done in those five pages. And, looking back, it was the best possible education that I could have had in how to construct a story."(pp21-22)

From 1980 through to 1984, Moore, who maintained his status as a freelance writer, was offered a spate of work by a variety of different comic book companies in Britain, namely 2000AD, Marvel UK and Warrior. He later remarked that "I remember that what was generally happening was that everybody wanted to give me work, for fear that I would just be given other work by their rivals. So everybody was offering me things."(p57) It was an era when comic books were increasing in popularity in Britain, and according to Lance Parkin, "the British comics scene was cohering as never before, and it was clear that the audience was sticking with the title as they grew up. Comics were no longer just for very small boys: teenagers - even A-level and university students - were reading them now."(p20)