Bloch was born in Chicago, the son of Raphael "Ray" Bloch (1884 - 1952), a bank cashier, and his wife Stella Loeb (1880 - 1944), a social worker, both of German-Jewish descent.

Bloch's first wife Marion Bloch was married in a ceremony which was basically a marriage of convenience to keep Bloch out of the army.

Bloch was close friends with C.L. Moore and her husband Henry Kuttner who visited him in Milwaukee.

Bloch died in 1994 in Los Angeles. He was cremated and interred in the Room of Prayer columbarium at Westwood Village Memorial Park Cemetery in Los Angeles.

During the 1930s, Bloch was an avid reader of the pulp magazine Weird Tales. H. P. Lovecraft, a frequent contributor to that magazine, became one of his favorite writers. As a teenager, Bloch befriended and corresponded with Lovecraft, who gave the promising youngster advice on his own fiction-writing efforts. Bloch's first professional sales, at the age of just seventeen, were to Weird Tales with the short stories "The Feast in the Abbey" and "The Secret in the Tomb". Bloch's early stories were strongly influenced by Lovecraft. Indeed, a number of his stories were set in, and extended, the world of Lovecraft's Cthulhu Mythos. It was Bloch who invented, for example, the oft-cited Mythos texts De Vermis Mysteriis and Cultes des Goules.

The young Bloch appears, thinly disguised, as the character "Robert Blake" in Lovecraft's story "The Haunter of the Dark", which is dedicated to Bloch. In this story, Lovecraft kills off the Bloch character, repaying a courtesy Bloch earlier paid Lovecraft with his tale "The Shambler from the Stars", in which the Lovecraft-inspired figure dies; the story goes so far as to use Bloch's then-current street address in Milwaukee. (Bloch even had a signed certificate from Lovecraft [and some of his creations] giving Bloch permission to kill Lovecraft off in a story.) Bloch later wrote a third tale, "The Shadow From the Steeple", picking up where "The Haunter of the Dark" finished. After Lovecraft's death in 1937, he continued writing for Weird Tales, where he became one of its most popular authors. He also began contributing to other pulps, such as the science fiction magazine Amazing Stories.

Bloch gradually evolved away from Lovecraftian imitations towards a unique style of his own. One of the first distinctly "Blochian" stories was "Yours Truly, Jack the Ripper", which was published in Weird Tales in 1943. The story was Bloch's take on the Jack the Ripper legend, and was filled out with more genuine factual details of the case than many other fictional treatments. It cast the Ripper as an eternal who must make human sacrifices to extend his immortality. It was adapted for both radio (in Stay Tuned for Terror) and television (as an episode of Thriller in 1961 written by Barré Lyndon). Bloch followed up this story with a number of others in a similar vein dealing with half-historic, half-legendary figures such as the Man in the Iron Mask ("Iron Mask", 1944), the Marquis de Sade ("The Skull of the Marquis de Sade", 1945) and Lizzie Borden ("Lizzie Borden Took an Axe...", 1946). Bloch also continued to revisit the Jack the Ripper theme. His contribution to Harlan Ellison's science fiction anthology, Dangerous Visions was a story, "A Toy for Juliette", which evoked both the Marquis de Sade and Jack the Ripper in a time-travel story. The same anthology had Ellison's sequel to it titled "The Prowler in the City at the Edge of the World". His earlier idea of the Ripper as an immortal being resurfaced in Bloch's contribution to the original Star Trek series episode Wolf in the Fold. His 1984 novel Night of the Ripper is set during the reign of Queen Victoria and follows the investigation of Inspector Abberline in attempting to apprehend the Ripper and includes some famous Victorians such as Sir Arthur Conan Doyle within the storyline.

Campaign manager for Carl Zeidler

In 1939, Bloch was contacted by James Doolittle, who was managing the campaign for a little-known assistant attorney in Milwaukee, Wisconsin named Carl Zeidler. He was asked to work on his speechwriting, advertising, and photo ops, in collaboration with Harold Gauer. They created elaborate campaign shows; in Bloch's 1993 autobiography, Once Around the Bloch, he gives an inside account of the campaign, and the innovations he and Gauer came up with — for instance, the original releasing-balloons-from-the-ceiling shtick. He comments bitterly on how, after Zeidler's victory, they were ignored and not even paid their promised salaries. He ends the story with a wryly philosophical point:

If Carl Zeidler had not asked Jim Doolittle to manage his campaign, Doolittle would never have contacted me about it. And the only reason Doolittle knew me to begin with was because he read my yarn ("The Cloak") in Unknown.

Rattling this chain of circumstances, one may stretch it a bit further. If I had not written a little vampire story called "The Cloak", Carl Zeidler might never have become mayor of Milwaukee.

Bloch became most famous as the author of the novel Psycho, one of the first examples of modern urban horror relying on realism rather than the supernatural, which was adapted by Joseph Stefano into the screenplay for the 1960 film of the same name, directed by Alfred Hitchcock. He had written an earlier split-personality short story, "The Real Bad Friend", which appeared in the February, 1957 Mike Shayne Mystery Magazine, that foreshadowed the 1959 novel Psycho.

In 1962 Bloch penned the story and teleplay The Sorceror's Apprentice for Alfred Hitchcock Presents. The episode was shelved when sponsor Revlon called its ending "too gruesome" (by 1960s standards) for airing. Bloch was pleased later when the episode was included in the program's syndication package to affiliate stations where not one complaint was registered. Today, due to public domain status, the episode is readily available in home media formats from numerous distributors and is even available on free video on demand.

His best-known work as a screenwriter is probably The Night Walker (1964), which he wrote for William Castle, although he also penned several scripts for the original series of Star Trek including "What Are Little Girls Made Of?", "Wolf in the Fold", and "Catspaw". He seemed happiest, among his television work, with his contributions to the Boris Karloff-hosted series Thriller.

An early reference work by Australia's Graeme Flanagan, Robert Bloch: A Bio-Bibliography (1979) includes valuable material including interviews with Bloch and memoirs by fellow writers such as Harlan Ellison, Mary Elizabeth Counselman and Fritz Leiber.

Randall D. Larson has authored three reference books about Robert Bloch: The Robert Bloch Reader's Guide (1986, a literary analysis of Bloch's entire output through 1986), The Complete Robert Bloch (1986, an illustrated bibliography of Bloch's writing), and The Robert Bloch Companion (1986, collected interviews). In addition, an issue of Paperback Parade magazine (No. 39, August 1994) contains two articles by Larson on collecting Bloch - "Paperblochs: Robert Bloch in Paperback" and "Robert Bloch in Paperback".

There is an essay on Bloch's work, with particular reference to the novels Psycho and The Scarf, in S. T. Joshi's book The Modern Weird Tale (2001). Joshi examines Bloch's literary relationship with Lovecraft in a further essay in The Evolution of the Weird Tale (2004).

A new essay collection focusing on a range of Bloch's work is Robert Bloch: the Man Who Collected Psychos, edited by Benjamin J. Szumskyj (McFarland, 2009).

Novels

• The Scarf (1947, rev. 1966)
• Spiderweb (1954)
• The Kidnapper (1954)
• The Will to Kill (1954)
• Shooting Star (1958) (note: published in a double volume with the ss collection Terror in the Night)
• This Crowded Earth (1958)
• Psycho (1959) (adapted into the 1960 film, Psycho, directed by Alfred Hitchcock; later remade in 1998 by Gus Van Sant)
• The Dead Beat (1960)
• Firebug (1961)
• The Couch (1962)
• Terror (1962)
• Ladies Day / This Crowded Earth (1968)
• The Star Stalker (1968)
• The Todd Dossier (1969)
• Sneak Preview (1971)
• It's All in Your Mind (1971)
• Night World (1972)
• American Gothic (1974)
• Strange Eons (1978) (a Cthulhu Mythos novel)
• There Is a Serpent in Eden (1979)
• Psycho II (1982) (unrelated to the film of the same name)
• Night of the Ripper (1984)
• Unholy Trinity (1986) (collects The Scarf, The Couch and The Dead Beat)
• Lori (1989)
• Three Novels of Suspense (collects The Will to Kill, Firebug and The Star Stalker)
• Psycho House (1990) (unrelated to the films Psycho II, Psycho III or The Beginning)
• The Jekyll Legacy (1991)
• Yours Truly, Jack the Ripper (1991) (Pulphouse; a 100-copy hardbound signed edition of Bloch's famous short story)
• The Thing (1993) (Pretentious Press; a limited edition of 85 copies, only 9 bound in cloth, of the author's first appearance in print - a parody of H.P. Lovecraft which originally appeared in the April 1932 issue of The Quill, his Lincoln High School literary magazine)
• Psycho - The 35th Anniversary Edition (1994) (Gauntlet Press; limited edition of 500 copies; the last work to be signed by Bloch before his death; includes a new intro by Richard Matheson and a new Afterword by Ray Bradbury)

Short-story collections

• The Thing (1932) actually a single short story, the authors first, but initially published in book form by The Pretentious Press in (1993)
• A Portfolio Of Some Rare And Exquisite Poetry By The Bard Of Bards (1937 or 1938) written under the pseudonym Sarcophagus W. Dribble. One page folded to make 4. Poetry.
• The Opener of the Way (1945)
• Sea Kissed (1945)
• Terror in the Night (1958) (note: published in a double volume with the novel Shooting Star)
• Nightmares (1960)
• Blood Runs Cold (1961)
• Nightmares (1961)
• More Nightmares (1961)
• Yours Truly, Jack the Ripper (1962)
• Atoms and Evil (1962)
• Horror 7 (1963)
• Bogey Men (1963)
• House of the Hatchet (1965)
• The Skull of the Marquis de Sade (1965)
• Tales in a Jugular Vein (1965)
• Chamber of Horrors (1966)
• The Living Demons (1967)
• Dragons and Nightmares (1968)
• Bloch and Bradbury (1969)
• Fear Today, Gone Tomorrow (1971)
• House of the Hatchet (1976)
• The King of Terrors (1977)
• The Best of Robert Bloch (1977)
• Cold Chills (1977)
• Out of the Mouths of Graves (1978)
• Such Stuff as Screams Are Made Of (1979)
• Mysteries of the Worm (1981)
• Midnight Pleasures (1987)
• Lost in Space and Time With Lefty Feep (1987)
• The Complete Stories of Robert Bloch: Volume 1: Final Reckonings (1987)
• The Complete Stories of Robert Bloch: Volume 2: Bitter Ends (1987)
• The Complete Stories of Robert Bloch: Volume 3: Last Rites (1987)
• Fear and Trembling (1989)
• Mysteries of the Worm (rev. 1993) from Chaosium books
• The Early Fears (1994)
• Flowers from the Moon and Other Lunacies (1998)
• The Lost Bloch: Volume 1: The Devil With You! (1999)
• The Lost Bloch: Volume 2: Hell on Earth (2000)
• The Lost Bloch: Volume 3: Crimes and Punishments (2002)
• The Reader's Bloch: Volume 1: The Fear Planet and Other Unusual Destinations (2005)
• The Reader's Bloch: Volume 2: Skeleton in the Closet and Other Stories (2009)

Non-fiction

• The Eighth Stage of Fandom (1962)
• Out of My Head (1986)
• Once Around the Bloch: An Unauthorized Autobiography (1993)
• Robert Bloch: Appreciations of the Master (1995)

MoviesThe following is a list of films based on Bloch's work. For some of these he wrote the original screenplay; for others, he supplied the story or a novel (as in the case of Psycho) on which the screenplay was based.

• Psycho (1960)
• The Couch (1962)
• The Cabinet of Caligari (1962)
• Strait-Jacket (1964)
• The Night Walker (1964)
• The Skull (1965)
• The Psychopath (1966)
• Torture Garden (1967)
• The Deadly Bees (1967)
• The House That Dripped Blood (1970)
• Asylum (1972)
• The Cat Creature (Tv movie 1973)
• The Dead Don't Die (Tv movie 1974)
• The Amazing Captain Nemo (1978)
• Psycho (1998)