Ellison was born to a Jewish family in Cleveland, Ohio, on May 27, 1934, the son of Serita (née Rosenthal) and Louis Laverne Ellison, a dentist and jeweler.
He had an older sister, Beverly (Rabnick), who was born in 1926.
She died in 2010 without having spoken to him since their mother's funeral in 1976.
His family subsequently moved to Painesville, Ohio, but returned to Cleveland in 1949, following his father's death.
Ellison frequently ran away from home (in an interview with Tom Snyder he would later claim it was due to discrimination by his high school peers), taking an array of odd jobs—including, by age 18, "tuna fisherman off the coast of Galveston, itinerant crop-picker down in New Orleans, hired gun for a wealthy neurotic, nitroglycerine truck driver in North Carolina, short-order cook, cab driver, lithographer, book salesman, floorwalker in a department store, door-to-door brush salesman, and as a youngster, an actor in several productions at the Cleveland Play House".
In 1947, a fan letter he wrote to Real Fact Comics became his first published writing.

Ellison attended Ohio State University for 18 months (1951–53) before being expelled.
He said the expulsion was for hitting a professor who had denigrated his writing ability, and over the next 20 or so years he sent that professor a copy of every story that he published.

Ellison published two serialized stories in the Cleveland News during 1949, and he sold a story to EC Comics early in the 1950s.
During this period, Ellison was an active and visible member of science fiction fandom, and published his own science fiction fanzines, such as Dimensions (which had previously been the Bulletin of the Cleveland Science Fantasy Society for the Cleveland Science Fantasy Society, and later Science Fantasy Bulletin.)
 Ellison moved to New York City in 1955 to pursue a writing career, primarily in science fiction.
Over the next two years, he published more than 100 short stories and articles.
The short stories collected as Sex Gang — which Ellison described in a 2012 interview as "mainstream erotica" — date from this period.

He served in the U.S. Army from 1957 to 1959.

His first novel, Web of the City, was published during his military service in 1958, and he said that he had written the bulk of it while undergoing basic training at Fort Benning, Georgia.

After leaving the army, he relocated to Chicago, where he edited Rogue magazine.
Ellison was born to a Jewish family in Cleveland, Ohio, on May 27, 1934, the son of Serita (née Rosenthal) and Louis Laverne Ellison, a dentist and jeweler. He had an older sister, Beverly (Rabnick), who was born in 1926. She died in 2010 without having spoken to him since their mother's funeral in 1976. His family subsequently moved to Painesville, Ohio, but returned to Cleveland in 1949, following his father's death. Ellison frequently ran away from home (in an interview with Tom Snyder he would later claim it was due to discrimination by his high school peers), taking an array of odd jobs—including, by age 18, "tuna fisherman off the coast of Galveston, itinerant crop-picker down in New Orleans, hired gun for a wealthy neurotic, nitroglycerine truck driver in North Carolina, short-order cook, cab driver, lithographer, book salesman, floorwalker in a department store, door-to-door brush salesman, and as a youngster, an actor in several productions at the Cleveland Play House". In 1947, a fan letter he wrote to Real Fact Comics became his first published writing.
Ellison attended Ohio State University for 18 months (1951–53) before being expelled. He said the expulsion was for hitting a professor who had denigrated his writing ability, and over the next 20 or so years he sent that professor a copy of every story that he published.
Ellison published two serialized stories in the Cleveland News during 1949, and he sold a story to EC Comics early in the 1950s. During this period, Ellison was an active and visible member of science fiction fandom, and published his own science fiction fanzines, such as Dimensions (which had previously been the Bulletin of the Cleveland Science Fantasy Society for the Cleveland Science Fantasy Society, and later Science Fantasy Bulletin.)  Ellison moved to New York City in 1955 to pursue a writing career, primarily in science fiction. Over the next two years, he published more than 100 short stories and articles. The short stories collected as Sex Gang — which Ellison described in a 2012 interview as "mainstream erotica" — date from this period.
He served in the U.S. Army from 1957 to 1959.
His first novel, Web of the City, was published during his military service in 1958, and he said that he had written the bulk of it while undergoing basic training at Fort Benning, Georgia.
After leaving the army, he relocated to Chicago, where he edited Rogue magazine.
Harlan Ellison