Davidson wrote many stories for fiction magazines beginning in the 1950s, after publishing his first fiction in Commentary and other Jewish intellectual magazines.

He was active in science fiction fandom from his teens. His best-known works are his novels about Vergil Magus, the magician that medieval legend made out of the Roman poet Virgil; the Peregrine novels, a comic view of Europe shortly after the fall of Rome; the Jack Limekiller stories about a Canadian living in an imaginary Central American country modelled after Belize during the 1960s, and the stories of Dr. Eszterhazy, a sort of even more erudite Sherlock Holmesian figure living in the mythical Scythia-Pannonia-Transbalkania, the waning fourth-largest empire in Europe.

In Joyleg, A Folly, written in collaboration with Ward Moore, a veteran of the American Revolutionary War (and of the Whiskey Rebellion) is found alive and very well in the Tennessee backwoods, having survived over the centuries by daily soaks in whisky of his own making to hilariously face the world of the 1960s.

Davidson also wrote dozens of short stories that defy classification, and the Adventures in Unhistory essays, which delve into puzzles such as the identity of Prester John and suggest solutions to them. His earlier historical essays were scrupulously researched, even when published by magazines just as happy to offer fiction as fact.

Very little may happen in a Davidson story, but he enjoyed describing it in enormous detail with many elements that beginning writers are told to avoid, such as page-long sentences with half a dozen colons and semi-colons, or an irrelevant digression in the opening pages of a story. Davidson success with this technique arose from his chutzpah and his skill with words and narrative structure, particularly a good ear for the way that people talk, an encyclopedic store of obscure and fascinating knowledge, and a comic view of the world that sees virtually everyone as eccentric.

The idea in his story "Or All the Seas with Oysters" (1958) is reputed to have become part of an urban legend in the street culture of some children; namely, that bicycles arise from a life cycle that involves paper clips as pupae and coat hangers as larvae. The English fantasy author Terry Pratchett reused the idea as a major plot-point in his Discworld novel Reaper Man.

Davidson was born in 1923 in Yonkers, New York. He served as a Navy hospital corpsman (medic) with the Marine Corps in the Pacific during World War II, and began his writing career as a Talmudic scholar around 1950. This made his study of and conversion to Tenrikyo in the 1970s rather surprising. Although he had a reputation for being quick to anger when anyone tampered with his work or misunderstood it, Davidson was also greatly in demand as a storyteller, and well-known among his friends for his extreme generosity.

He was a member of the Swordsmen and Sorcerers' Guild of America , a loose-knit group of Heroic Fantasy authors founded in the 1960s, some of whose works were anthologized in Lin Carter's Flashing Swords! anthologies.

While editing The Magazine of Fantasy and Science Fiction he lived in Mexico, and later in British Honduras (now renamed Belize). He lived in a rural district of Novato, in northern Marin County, California, in 1970, but later moved closer to San Francisco. He lived in a small house in Sausalito, at the southern end of Marin County next to San Francisco in 1971 and 1972, and it was there fans and friends were affectionately welcomed. In his later years, he lived in Washington state, including a brief stay in the Veterans' Home in Bremerton. He died in his tiny apartment in Bremerton on May 8, 1993, aged 70. A memorial service was held in Gasworks Park in Seattle.

He was survived by his son Ethan and his ex-wife Grania Davis, who continues to edit and release his unpublished works.

Doctor Eszterhazy series

The Adventures of Doctor Eszterhazy, Owlswick Press, 1990; includes all but one of the published Doctor Eszterhazy stories.

"The Odd Old Bird" in The Other Nineteenth Century

Limekiller series

Limekiller, Old Earth Books, 2003; includes all of the published Limekiller stories

Vergil Magus series

The Phoenix and the Mirror, Doubleday, 1969; the first Vergil Magus novel

Vergil in Averno, Doubleday, 1987; the second Vergil Magus novel

The Scarlet Fig; or Slowly through a Land of Stone; Rose Press, 2005, the third Vergil Magus novel

"The Other Magus," in Edges, edited by Ursula K. Le Guin and Virginia Kidd, Pocket Books; Berkley paperback, 1980

"Vergil and the Caged Bird," Amazing, January 1987

"Vergil and the Dukos: Hic Inclusus Vitam Perdit, or The Imitations of the King," Asimov's, September 1997, pp. 102—113

"Vergil Magus: King without Country," with Michael Swanwick, Asimov's, July 1998

Peregrine series

Peregrine: Primus, Walker, 1969

Peregrine: Secundus, Berkley paperback, 1981

Novels

Clash of Star-Kings, Ace double, 1966

The Enemy of My Enemy, Berkley paperback, 1966

The Island Under the Earth, Ace paperback, 1969

The Kar-Chee Reign, Ace double, 1966

Masters of the Maze, Pyramid paperback, 1965

Mutiny in Space, Pyramid Books, 1964

Rogue Dragon, Ace paperback, 1966

Rork!, Berkley Medallion paperback, 1965

Ursus of Ultima Thule, Avon paperback, 1973

With Grania Davis

The Boss in the Wall, A Treatise on the House Devil, Tachyon Publications, 1998

Marco Polo and the Sleeping Beauty, Baen Books paperback, 1987

With Harlan Ellison

"Up Christopher to Madness," Knight Magazine, 1965

With Ward Moore

Joyleg, A Folly, Pyramid paperback, 1962

Collections

Or All the Seas with Oysters, Berkely Books, 1962

Strange Seas and Stories, Doubleday, 1971

Adventures in Unhistory, Owlswick Press, 1993

The Avram Davidson Treasury, Tor, 1998

The Investigations of Avram Davidson, Owlswick Press, 1999

Everybody Has Somebody in Heaven, Devora Publishing, 2000

The Other Nineteenth Century, Tor, 2001

Ellery Queen books - the novels written based on outlines by Frederic Dannay, one of the cousins who created "Ellery Queen"

And on the Eighth Day, Random House, 1964

The Fourth Side of the Triangle, Random House, 1965