Klein was born and lives in New York City and attended Brown University where he wrote his honors thesis on H. P. Lovecraft, edited the Brown Daily Herald and graduated Phi Beta Kappa in 1969. In the 1970s, he studied film history at Columbia University, wrote short fiction and non-fiction and worked as a movie script reader for Paramount Pictures.

He was the editor of Twilight Zone magazine from its inception in 1981 until 1985, and served as editor of the short-lived true crime magazine CrimeBeat from 1991 to 1993. He has also taught English at New York's John Jay College and been a long time supporter of animal rights.

He added "Eibon" to his name--a reference to Clark Ashton Smith's Hyperborean wizard--so that when he used his initials in his byline, ala H. P. Lovecraft or M. R. James, they would spell out his nickname "Ted".

Klein has blamed his limited output of fiction on writer's block. He revealed in the book Faces of Fear (1985) that he had struggled with The Ceremonies for more than five years before finally finishing it, adding: "I'm one of those people who will do anything to avoid writing. Anything!"

He first attracted notice with the novella "The Events at Poroth Farm" (1972), in which a college lecturer, isolated in the countryside and reading horror literature for teaching in the next semester, gradually realises that genuine supernatural horror is taking place around him. The story is notable for the insidious way in which the narrator's responses to the works he is reading (including those of Charles Robert Maturin, Ann Radcliffe, Monk Lewis, Le Fanu, Bram Stoker, Aleister Crowley, and Shirley Jackson) are conflated with his impressions of the supernatural threat.

In 1984 Klein published the novel The Ceremonies, which uses the same basic plot as the novella to more expansive ends; the threat this time is not to one man or one community, but to the entire world. The Ceremonies takes up and elaborates upon some of the mysteries of Arthur Machen's story "The White People" and is called "a modern classic" in an essay by Thomas F. Monteleone in the book Horror: 100 Best Books. A second novel, Nighttown, was announced by Klein soon afterwards and described by him in Faces of Fear as "a paranoid horror novel set entirely in New York City", but has not appeared.

In 1985 Klein published the collection Dark Gods, which includes four novellas:

• "Children of the Kingdom", set in part during the New York City blackout of 1977, and which dealt with hollow earth lore and hostile creatures hiding in the shadows of New York; first published in the anthology Dark Forces;
• "Petey", about a madman's monstrous "pet" which brings a well-to-do, middle-class housewarming to an unpleasant conclusion;
• "Black Man with a Horn", a tale in the vein of Lovecraft which treats of an elderly horror writer (modelled on Frank Belknap Long) and his discoveries about the dreaded Tcho-Tcho people;
• and "Nadelman's God", about a man who finds that an overwrought poem he wrote as an adolescent has been used as an incantation to bring a monstrous deity to life.

Klein also wrote the screenplay for Dario Argento's 1993 film Trauma, which starred Asia Argento and Piper Laurie.

Klein has written two critical essays on weird fiction: Dr Van Helsing's Handy Guide to Ghost Stories (1981), a series of articles for Twilight Zone magazine; and Raising Goosebumps for Fun and Profit (1988), originally written for Writer's Digest. A critical essay on Klein's own work can be found in S. T. Joshi's book.

Novels

• The Ceremonies (Viking 1984, Bantam 1985, Pan (UK) 1985)
• Excerpt in A Fantasy Reader: The Seventh World Fantasy Convention Book, ed. Jeff Frane & Jack Rems, 1981
• Excerpt in The Bantam Sampler: Summer '85, Bantam 1985
• German-language reprint, MorgenGraun, Goldmann Verlag 1986
• Outtake in Dagon #18/19, 1987

Collections

• Dark Gods (Viking 1985, Bantam 1986, Pan (UK) 1987)

Contents:

"Children of the Kingdom"

"Petey"

"Black Man with a Horn"

"Nadelman's God"

• German-language reprint, Verschwörung der Götter, Goldmann Verlag 1987
• Reassuring Tales Subterranean Press, 2006

Contents:

"Introduction"

"Camera Shy"

"Growing Things"

"Curtains for Nat Crumley"

"Magic Carpet"

"One Size Eat All"

"Ladder"

"Well-Connected"

"S.F."

"They Don't Write 'Em Like This Anymore"

"The Events at Poroth Farm"

Chapbooks

• Raising Goosebumps for Fun and Profit (Footsteps Press 1989)
• Nonfiction expansion of "Horrors!: An Introduction to Writing Horror Fiction", which first appeared in The Secrets of Writing Popular Fiction, Writer's Digest 1986.
• The Events at Poroth Farm (Necronomicon Press 1990)
• Revised version of 1972 novella with an introduction by the author.

Short fiction

• "The Events at Poroth Farm" (From Beyond the Dark Gateway #2, December 1972)
• Reprinted (revised) in The Year's Best Horror Stories, No. 3, ed. Richard Davis, Sphere (UK) 1973
• Reprinted (revised again) in The Year's Best Horror Stories: Series II, ed. Richard Davis, DAW 1974
• Reprinted (revised yet again) in First World Fantasy Awards, ed. Gahan Wilson, Doubleday 1977
• Reprinted (revised a final time) as a Necronomicon Press chapbook, 1990
• Reprinted in A Century of Horror 1970-1979, ed. David Drake & Martin H. Greenberg, MJF Books 1996
• Reprinted in Return to Lovecraft Country, ed. Scott David Aniolowski, Triad Entertainments 1997
• Reprinted in Eternal Lovecraft: The Persistence of H.P. Lovecraft in Popular Culture, ed. Jim Turner, Golden Gryphon Press 1998
• Reprinted in Reassuring Tales, Subterranean Press 2006
• Reprinted in American Supernatural Tales, ed. S. T. Joshi, Penguin Books 2007
• "Renaissance Man" (Space 2, ed. Richard Davis, Abelard-Schumann (UK) 1974)
• Reprinted in Microcosmic Tales, ed. Isaac Asimov, Martin H. Greenberg and Joseph D. Olander, Taplinger 1980)
• "S.F." (The Year's Best Horror Stories: Series III, ed. Richard Davis, DAW 1975)
• Reprinted in The First Orbit Book of Horror Stories, ed. Richard Davis, Futura (UK) 1976
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "Magic Carpet" (Myrddin #3, 1976)
• Reprinted in Spectre 4, ed. Richard Davis, Abelard-Schumann (UK) 1977
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "Petey" (Shadows 2, ed. Charles L. Grant, Doubleday 1979, Berkley 1984)
• Reprinted in The Dodd, Mead Gallery of Horror, ed. Charles L. Grant, Dodd Mead 1983
• Reprinted in Dark Gods, Viking 1985
• Reprinted in Meddling with Ghosts, ed. Ramsey Campbell, The British Library 2001
• "Black Man with a Horn" (New Tales of the Cthulhu Mythos, ed. Ramsey Campbell, Arkham House 1980)
• Reprinted in The Year's Best Horror Stories: Series IX, ed. Karl Edward Wagner, DAW 1981
• Reprinted in Dark Gods, Viking 1985
• Reprinted in Horrorstory Volume Three, ed. Karl Edward Wagner, Underwood-Miller 1992
• Reprinted in Cthulhu 2000: A Lovecraftian Anthology, ed. Jim Turner, Arkham House 1995
• "Children of the Kingdom" (Dark Forces, ed. Kirby McCauley, Viking 1980, Bantam 1981, Macdonald Futura (UK) 1980, Futura (UK) 1981)
• Reprinted in Dark Gods, Viking 1985
• Reprinted in 13 Short Horror Novels, ed. Charles G. Waugh & Martin H. Greenberg, Crown/Bonanza 1987
• "Camera Shy" (sold to Close-Up Polaroid Corp., 1980, but was not published at that time)
• First published in Crypt of Cthulhu #56, 1988
• Reprinted in 100 Vicious Little Vampire Stories, ed. Robert Weinberg, Stefan Dziemianowicz & Martin H. Greenberg, Barnes & Noble 1995
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "Nadelman's God" (Dark Gods, Viking 1985)
• Reprinted in The Mammoth Book of Short Horror Novels, ed. Mike Ashley, Robinson 1988
• "Well-Connected" (as "Hagendorn's House") (Country Inns, Spring 1987)
• Reprinted in Dagon #18/19, 1987
• Reprinted in Weird Tales, Spring 1988
• Reprinted in Best of Weird Tales, ed. John Betancourt, Barnes & Noble 1995
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "They Don't Write 'em Like This Anymore" (screen treatment) (Pulp Magazine, March 1989)
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "Ladder" (Borderlands, ed. Thomas F. Monteleone, Avon 1990)
• Reprinted in The Year's Best Fantasy and Horror: Fourth Annual Collection, ed. Ellen Datlow & Terri Windling, St. Martin's 1991
• Reprinted in The Best of Borderlands, ed. Thomas F. Monteleone & Elizabeth E. Monteleone, Borderlands Press 2005
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "One Size Eats All" (Outside Kids, Summer 1993)
• Reprinted in The Best New Horror: Volume Five, ed. Stephen Jones & Ramsey Campbell, Raven 1994
• Reprinted in The Year's Best Horror Stories: XXII, ed. Karl Edward Wagner, DAW 1994
• Reprinted in 100 Tiny Tales of Terror, ed. Robert Weinberg, Stefan R. Dziemianowicz & Martin H. Greenberg, Barnes & Noble 1996
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "Curtains for Nat Crumley" (Gahan Wilson's The Ultimate Haunted House, ed. Gahan Wilson, HarperPrism 1996)
• Reprinted in Reassuring Tales, Subterranean Press 2006
• "Growing Things" (999: New Stories of Horror and Suspense, ed. Al Sarrantonio, Avon 1999)
• Reprinted in The Mammoth Book of Best New Horror: Volume Eleven, ed. Stephen Jones, Robinson 2000
• Reprinted in Reassuring Tales, Subterranean Press 2006

Poetry

• "Lament of an Aging English Instructor" (Bardic Echoes, Vol. XIII, No. 1, March 1972)
• "The Paintings of Hieronymous Bosch" (Nyctalops #8, April 1973)
• "The Father of the Witch" (Nyctalops #8, April 1973)
• "The Book of Hieronymous Bosch" (Twilight Zone, February 1988)

Nonfiction (incomplete)

• "Summer Reading" (Scrutinize, Vol. II, No. 2, Summer 1964)
• Material in Brown Daily Herald, Brown University, 1966-1969 (film reviewer, arts editor, editor in chief)
• Material in The Brown Jug, Brown Review, Taliesin and other college publications, 1966-1969
• "The Liberal Arts Syndrome" (New York Daily Column, May 8, 1968)
• Chapter on Brown University in The Ivy League Guidebook by Andrew Tobias, Arnold Bortz, and Caspar Weinberger, Jr. (Collier 1969)
• Film reviews in Columbia Spectator, Columbia University, 1970-1971
• "Charles Manson, B.M.O.C." (New York Times, March 28, 1972)
• "They Kill Animals and They Call It Art" (New York Times, January 13, 1974)
• "The Festival" (The First World Fantasy Convention, bound with essays by Robert Bloch and Fritz Leiber in a special hardcover edition of Science-Fantasy Correspondent: One, ed. Willis Conover, Carrollton-Clark 1975)
• Reprinted in The First World Fantasy Convention: Three Authors Remember, Necronomicon Press 1976
• "Animals in Movies - The Abuse Gets Worse" (New York Times, June 8, 1975)
• "How I Flopped as a Paramount Scriptreader" (New York Times, October 26, 1975)
• Foreword to Writings in The United Amateur by H. P. Lovecraft (Necronomicon Press 1976)
• Story notes for Beyond Midnight, ed. Kirby McCauley (Berkley 1976)
• Foreword to The Old Gent by Willis Conover (Conover 1977)
• "Ramsey Campbell: An Appreciation" (Nyctalops #13, May 1977)
• Reprinted in Fantasy Reader's Guide to Ramsey Campbell, ed. Mike Ashley (Cosmos Literary Agency 1980)
• Review of Legion by William Peter Blatty (Washington Post, July 4, 1983)
• Review of The Face That Must Die and Incarnate by Ramsey Campbell (Washington Post Book World, November 20, 1983)
• Contribution to "First Novelists" symposium in Library Journal, March 15, 1984
• Reprinted in Contemporary Literary Criticism
• Review of The Suburbs of Hell by Randolph Stow (Washington Post Book World, August 19, 1984)
• Biographical introduction to The Scarlet Letter by Nathaniel Hawthorne (Readers Digest 1984)
• Afterword to A Connecticut Yankee in King Arthur's Court by Mark Twain (Readers Digest 1984)
• "Star Wares" (sic) (New York Daily News, December 2, 1984)
• "Master of a Lost Art" (New York Daily News, June 30, 1985)
• Review of The Glamour by Christopher Priest (Washington Post Book World, July 7, 1985)
• "Living Room Chills" (New York Daily News, September 22, 1985)
• Introduction to Slow by Ramsey Campbell (Footsteps Press 1986)
• Introduction to Stories from the Twilight Zone by Rod Serling (Bantam 1986)
• Introduction ("A Dreamer's Tales") to Dagon and Other Macabre Tales by H. P. Lovecraft (Arkham House 1986)
• "Horrors!: An Introduction to Writing Horror Fiction" (The Secrets of Writing Popular Fiction, Writer's Digest 1986)
• Essay "The House of Souls" by Arthur Machen Horror: 100 Best Books (Xanadu Publications 1988)
• Expanded as Raising Goosebumps for Fun and Profit (Footsteps Press 1989)
• "Minor Details: H. P. Lovecraft" (New England Monthly, August 1986)
• Twenty-five articles in The Penguin Encyclopedia of Horror and the Supernatural, edited by Jack Sullivan (Viking 1986): "Arkham House", "Charles Birkin", "William Peter Blatty", "Anthony Boucher", "Fredric Brown", "Robert W. Chambers", "John Collier", "Basil Copper", "W. F. Harvey", "Robert S. Hichens", "William Hope Hodgson", "Jerome K. Jerome", "Henry Kuttner", "Jack London", "Kirby McCauley", "Arthur Machen", "John Metcalfe", "Saki (H. H. Munro)", "Steven Spielberg", "The Supernatural: Belief and the Writer", "The Twilight Zone", "Edward Lucas White", "Henry S. Whitehead", "Colin Wilson"
• Introduction to Reassuring Tales (Subterranean Press 2006)

Screenplays

• Trauma (1993), with Dario Argento, based on a story by Argento, Franco Ferrini, and Gianni Romoli