Montague Summers was the youngest of the seven children of Augustus William Summers, a rich banker and justice of the peace in Clifton, Bristol. Summers was educated at Clifton College before studying theology at Trinity College, Oxford with the intention of becoming a priest in the Church of England. In 1905 he received a fourth-class Bachelor of Arts degree. He then continued his religious training at the Lichfield Theological College.

Summers was ordained as deacon in 1908 and worked as a curate in Bath and Bitton, in Greater Bristol. He never proceeded to higher orders, however, probably because of rumours of his interest in Satanism and accusations of sexual impropriety with young boys, for which he was tried and acquitted. Summer's first book, Antinous and Other Poems, published in 1907, was dedicated to the subject of pederasty.

Summers also joined the growing ranks of English men of letters interested in medievalism, Catholicism, and the occult. In 1909 he converted to Catholicism and shortly thereafter he began passing himself off as a Catholic priest and styling himself the "Reverend Alphonsus Joseph-Mary Augustus Montague Summers", even though he was never a member of any Catholic order or diocese. Whether he was ever actually ordained as a priest is a matter of dispute.

Summers worked for several years as an English and Latin teacher at various schools, including Brockley County School in south-east London, before adopting writing as his full-time employment. He was interested in the theater of the seventeenth century, particularly that of the English Restoration, and edited the plays of Aphra Behn, John Dryden, William Congreve, among others. He was one of the founder members of The Phoenix, a society that performed those neglected works, and was elected a fellow of the Royal Society of Literature in 1916.

Montague Summers also produced important studies of the Gothic fiction genre and edited two collections of Gothic horror short stories, as well as an incomplete edition of two of the seven obscure Gothic novels, known as the Northanger Horrid Novels, mentioned by Jane Austen in her Gothic parody Northanger Abbey. He was instrumental in rediscovering those lost works, which some had supposed were an invention of Jane Austen herself. He also published biographies of writers Jane Austen and Ann Radcliffe.

Summer's career as an ostensibly Catholic clergyman was highly unusual. He wrote works of hagiography on Saint Catherine of Siena and Saint Anthony Maria Zaccaria, but his primary religious interest was in the subject of the occult. While Aleister Crowley, with whom he was acquainted, adopted the persona of a modern-day witch, Summers played the part of the learned Catholic witch-hunter. In the introduction to his book on The History of Witchcraft and Demonology (1927) he writes:

In the following pages I have endeavored to show the witch as she really was – an evil liver: a social pest and parasite: the devotee of a loathly and obscene creed: an adept at poisoning, blackmail, and other creeping crimes: a member of a powerful secret organization inimical to Church and State: a blasphemer in word and deed, swaying the villagers by terror and superstition: a charlatan and a quack sometimes: a bawd: an abortionist: the dark counselor of lewd court ladies and adulterous gallants: a minister to vice and inconceivable corruption, battening upon the filth and foulest passions of the age.

In 1928, he published the first English translation of Heinrich Kramer's and James Sprenger's Malleus Maleficarum ("The Hammer of Witches"), a 15th century Latin text on the hunting of witches. In his introduction, Summers insists that the reality of witchcraft is an essential part of Catholic doctrine, and declares the Malleus to be an admirable and correct account of witchcraft and of the methods necessary to combat it. This should be contrasted with the vastly more skeptical and critical attitude of mainstream Catholic scholars, reflected for instance in the Rev. Herbert Thurston's article on "Witchcraft" for the Catholic Encyclopaedia of 1912, which labels the publication of the Malleus a "disastrous episode."

Montague Summers then turned to vampires, producing The Vampire: His Kith and Kin (1928) and The Vampire in Europe (1929), and later to werewolves with The Werewolf (1933). Summers's work on the occult is notorious for his unusual and old-fashioned writing style, his display of erudition, and his purported belief in the reality of the subjects he treats.

Summers cultivated his reputation for eccentricity. The Times of London wrote he was "in every way a 'character' and in some sort a throwback to the Middle Ages." His biographer, Brocard Sewell (writing under the pseudonym "Joseph Jerome"), paints the following portrait of Summers:

During the year 1927, the striking and somber figure of the Reverend Montague Sommers in black soutane and cloak, with buckled shoes--a la Louis Quatorze--and shovel hat could often have been seen entering or leaving the reading room of the British Museum, carrying a large black portfolio bearing on its side a white label, showing in blood-red capitals, the legend 'VAMPIRES'.

Despite his conservative religiosity, Summers was an active member of both the British Society for the Study of Sex Psychology, to which he contributed an essay on the Marquis de Sade, and of the Order of Chaeronea, a secret society which cultivated a pederastic homosexual ethos. Summers' interests also show in his edition of the poems of the sixteenth century poet Richard Barnfield, which partly are openly homosexual.

Montague Summers died at his home in Richmond, Surrey in August 1948. An autobiography The Galanty Show was published posthumously in 1980, though much is left unrevealed about his life.

Books on the occult

• The History of Witchcraft and Demonology, 1926
• The Geography of Witchcraft, 1927 (reprinted ISBN 0-7100-7617-7)
• His Kith and Kin, 1928 (reprinted by Senate in 1993 as simply The Vampire; reprinted with alternate title: Vampires and Vampirism ISBN 0-486-43996-8)
• The Vampire in Europe, 1929 (reprinted ISBN 0-517-14989-3) (reprinted with alternate title: The Vampire in Lore and Legend ISBN 0-486-41942-8)
• The Werewolf, 1933 (reprinted with alternate title: The Werewolf in Lore and Legend ISBN 0-486-43090-1)
• A Popular History of Witchcraft, 1937
• Witchcraft and Black Magic, 1946 (reprinted ISBN 1-55888-840-3, ISBN 0-486-41125-7)
• The Physical Phenomena of Mysticism, 1947

Poetry and drama

• Antinous and Other Poems, 1907
• William Henry (play), 1939
• Edward II (play), 1940

Fiction

• The Grimoire and Other Supernatural Stories, 1936
• Supernatural Tales, 1947

Other books

• St. Catherine of Siena, 1903
• Lourdes, 1904
• A Great Mistress of Romance: Ann Radcliffe, 1917
• Jane Austen, 1919
• St. Antonio-Maria Zaccaria, 1919
• Architecture and the Gothic Novel, 1931
• The Restoration Theatre, 1934
• Essays in Petto 1933
• The Playhouse of Pepys, 1935
• The Gothic Quest: a History of the Gothic Novel 1938
• A Gothic Bibliography 1940

As editor or translator

• Works of Mrs. Aphra Behn, 1915
• Complete Works of Congreve, 1923
• Complete Works of Wycherley, 1924
• The Castle of Otranto by Horace Walpole, 1924
• The Complete Works of Thomas Shadwell, 1927
• Covent Garden Drollery, 1927
• Horrid Mysteries by the Marquis de Grosse 1927 (part of an incomplete edition of the Northanger Horrid Novels).
• The Necromancer; or, The Tale of the Black Forest by 'Ludwig Flammenberg' 1927 (part of an incomplete edition of the 'Northanger Horrid Novels').
• Demoniality by Lodovico Maria Sinistrati, 1927
• The Malleus Maleficarum of Heinrich Kramer and Jacob Sprenger, 1928
• The Discovery of Witches, 1928 by Matthew Hopkins (reprinted ISBN 0-404-18416-2)
• Compendium Maleficarum by Francesco Maria Guazzo, translated by E.A. Ashwin, 1929
• Demonolatry by Nicolas Remy, translated by E.A. Ashwin, 1930
• The Supernatural Omnibus, 1931 (reprinted ISBN 0-88356-037-2)
• Victorian Ghost Stories, 1936
• The Poems of Richard Barnfield, 1936
• The Complete Works of Thomas Otway, 1936