Offutt has been married for over 50 years to Jodie McCabe Offutt of Lexington, Kentucky. They have four children; author Chris Offutt, Jeff Offutt, Professor of Computer Science at George Mason University, Scotty Hyde, copy editor for the Park City Daily News in Bowling Green, Kentucky, and Melissa Offutt, who is a sales executive for Sprint in San Diego. Offutt also has five grandchildren.

Offutt began publishing in 1954 with the story "And Gone Tomorrow" in If. Despite this early sale, he doesn't consider his professional life to have begun until he sold the story "Blacksword" to Galaxy in 1959. His first true SF novel was Evil Is Live Spelled Backwards in 1970. Offutt disliked the title of this book, calling it "embarrassingly amateur".

Offutt has written and published numerous novels and short stories, including several in the "Thieves World" series edited by Robert Lynn Asprin and Lynn Abbey, which feature his best known character, the thief, Hanse, also known as Shadowspawn (and, later, Chance). His "Iron Lords" series, likewise, was popular. Offutt also wrote two series of books based on characters by Robert E. Howard, one on Howard's best known character, Conan, and one on a lesser known character, Cormac mac Art. He also wrote the 19-book science fiction "Spaceways" series, over half of which were collaborations.

As an editor Offutt produced a series of five anthologies entitled Swords Against Darkness, which included the first professional sale by Charles de Lint. From 1976 to 1978 he served as president of the Science Fiction Writers of America (SFWA).

Offutt also wrote a large number of pornographic/erotic works under twelve different pseudonyms, not all of them identified. Known pseudonyms include John Cleve, J.(John) X. Williams, Jeff Douglas, Turk Winter, Farrah Fawkes, & Baxter Giles. His main works in this area include the historical "Crusader" series.

Thieves' World

• Shadowspawn (1987)
• Deathknight (1990)
• The Shadow of Sorcery (1993)

War of the Gods on Earth

• The Iron Lords (1979)
• Shadows Out of Hell (1980)
• The Lady of the Snowmist (1983)

War of the Wizards

• Demon in the Mirror (1977) (with Richard K. Lyon)
• The Eyes of Sarsis (1980) (with Richard K. Lyon)
• Web of the Spider (1981) (with Richard K. Lyon)

Conan

• Conan and the Sorcerer (1978)
• The Sword of Skelos (1979)
• Conan the Mercenary (1980)

Cormac Mac Art

• Sword of the Gael (1975)
• The Undying Wizard (1976)
• The Sign of the Moonbow (1977)
• The Mists of Doom (1977)
• When Death Birds Fly (1980) (with Keith Taylor)
• The Tower of Death (1982) (with Keith Taylor)

Non-series novels

• Evil is Live Spelled Backwards (1970)
• The Great 24 Hour "Thing" (1971)
• The Chamber of Pleasures (1971)
• The Castle Keeps (1972)
• The Galactic Rejects (1973)
• Messenger of Zhuvastou (1973)
• Ardor on Aros (1973)
• Operation: Super Ms. (1974)
• The Black Sorcerer of the Black Castle (1974) [short story]
• Genetic Bomb (1975) (with D. Bruce Berry)
• Chieftain of Andor (1976; aka Clansman of Andor)
• My Lord Barbarian (1977)
• Rails Across the Galaxy (1982, magazine publication only) (with Richard Lyon)

Edited works

• Swords Against Darkness (1977)
• Swords Against Darkness II (1977)
• Swords Against Darkness III (1978)
• Swords Against Darkness IV (1979)
• Swords Against Darkness V (1979)

Works written under pseudonyms

Spaceways

• Of Alien Bondage (1982) (as John Cleve)
• Corundum's Woman (1982) (as John Cleve)
• Escape from Macho (1982) (as John Cleve)
• Satana Enslaved (1982) (as John Cleve)
• Master of Misfit (1982) (as John Cleve)
• Purrfect Plunder (1982) (as John Cleve)
• The Manhuntress (1982) (with Geo. W. Proctor as by John Cleve)
• Under Twin Suns (1982) (as John Cleve)
• The Quest of Qalara (1982) (as John Cleve)
• The Yoke of Shen (1983) (with Geo. W. Proctor as by John Cleve)
• The Iceworld Connection (1983) (with Jack C. Haldeman II and Vol Haldeman as by John Cleve)
• Star Slaver (1983) (with G. C. Edmondson as by John Cleve)
• Jonuta Rising! (1983) (with Victor Koman as by John Cleve)
• Assignment - Hellhole (1983) (with Roland J. Green as by John Cleve)
• Starship Sapphire (1983) (with Robin Kincaid as by John Cleve)
• The Planet Murderer (1984) (with Dwight V. Swain as by John Cleve)
• The Carnadyne Horde (1984) (with Victor Koman as by John Cleve)
• Race Across the Stars (1984) (with Robin Kincaid as by John Cleve)
• King of the Slavers (1984) (as John Cleve)

Crusader

• The Accursed Tower (1974) (as John Cleve)
• The Passionate Princess (1974) (as John Cleve)
• The Crusader: Books I and II (omnibus) (1980) (as John Cleve)
• Julanar The Lioness (1975) (as John Cleve)
• My Lady Queen (1975) (as John Cleve)
• The Crusader: Books III and IV (omnibus) (1981) (as John Cleve)
• Saladin's Spy (1986) (as John Cleve)

Non-series novels

• Slave of the Sudan (1969) (as John Cleve)
• Barbarana (1970) (as John Cleve)
• Call me Calamity (1970) (as John Cleve) (Calamity #1)
• Captives in the Chateau de Sade (1970) (as John Cleve)
• Manlib! (1970) (as John Cleve)
• The Devoured (1970) (as John Cleve)
• Fruit of the Loins (1970) (as John Cleve)
• Jodinareh (1970) (as John Cleve)
• The Juice of Love (1970) (as John Cleve) (Calamity #2)
• The Balling Machine (1971) (with D. Bruce Berry as by Jeff Douglas)
• The Sex Pill (1971) (as J. X. Williams)
• Holly Would (1973) (as John Cleve)
• Every Inch a Man (1974) (as John Cleve)
• A Vacation in the Erogenous Zones (1974) (as John Cleve)
• The Sexorcist (1974; aka Unholy Revelry) (as John Cleve)
• Punished Publisher (1975) (as John Cleve)

Non-fiction works

• The Complete Couple (1976) (as John Cleve; "with Jane Cleve")