Born and raised in Leicester, England, Wilson left school at 16. He worked in factories and at various occupations, and read in his spare time. Gollancz published the then 24-year-old Wilson's The Outsider in 1956; the work examines the role of the social "outsider" in seminal works of various key literary and cultural figures. These include Albert Camus, Jean-Paul Sartre, Ernest Hemingway, Hermann Hesse, Fyodor Dostoyevsky, William James, T. E. Lawrence, Vaslav Nijinsky and Vincent Van Gogh; Wilson discusses his perception of social alienation in their work. The book became a best-seller and helped popularize existentialism in Britain. Critical praise proved short-lived, however, and Wilson soon faced widespread criticism.
After the initial success of Wilson's first work, critics universally panned Religion and the Rebel (1957). Time magazine published a review, headlined "Scrambled Egghead", that pilloried the book.
Wilson has written non-fiction books on metaphysical and occult themes. In 1971, he published The Occult: A History featuring exegesis on Aleister Crowley, G. I. Gurdjieff, Helena Petrovna Blavatsky, Kabbalah, primitive magic, Franz Anton Mesmer, Gregor Rasputin, Daniel Dunglas Home, and Paracelsus (among others). He also wrote a markedly unsympathetic biography of Crowley, Aleister Crowley: The Nature of the Beast, and has written biographies on other spiritual and psychological visionaries, including Gurdjieff, C.G. Jung, Wilhelm Reich, Rudolf Steiner, and P.D. Ouspensky. He has also written non-fiction books on crime, ranging from encyclopedias to studies of serial killing. He has an ongoing interest in the life and times of Jack the Ripper and in sex-crime in general.
Wilson explored his ideas on human potential and consciousness in fiction, mostly detective fiction or science fiction, including several Cthulhu Mythos pieces.
Like his non-fiction work, much of Wilson's fictional output from Ritual in the Dark (1960) onwards has concerned itself with the psychology of murder — especially that of serial killing. However, he has also written science fiction of a philosophical bent, including the Spider-World series.
In The Strength to Dream (1961) Wilson attacked H.P. Lovecraft as "sick" and as "a bad writer" who had "rejected reality" — but he grudgingly praised Lovecraft's story "The Shadow Out of Time" as capable science-fiction. August Derleth, incensed by Wilson's treatment of Lovecraft in The Strength to Dream, then dared Wilson to write what became The Mind Parasites — to expound his philosophical ideas in the guise of fiction. Wilson also discusses Lovecraft in Order of Assassins (1972) and in the prefatory note to The Philosopher's Stone (1969). His short novel The Return of the Lloigor (1969/1974) also has roots in the Cthulhu Mythos - its central character works on the real book the Voynich Manuscript but discovers it to be a mediaeval Arabic version of the Necronomicon - as does his 2002 novel The Tomb of the Old Ones.