Judith Merril was born Judith Grossman on January 21, 1923 in Boston, Massachusettes. Growing up during the Great Depression was difficult for her family, and her father committed suicide during this time. Because of this, Merril moved with her mother to the Bronx, New York City in 1936 where her mother got a job at the Bronx House, a halfway house for homeless children. Growing up, Merril was a devout Zionist, and when that movement lost its appeal to her, she became active in Trotskyist activities. When she was seventeen, Merril met her first husband, Dan Zissman, at a Trotskyist Fourth of July picnic and they were married in October of 1940. Their daughter, Merril, was born in December of 1942, and Dan was drafted soon after. The two of them separated, however, and Merril took her daughter's name as her pen name ("Time Chronology").

In 1948 Merril's first story, "That Only A Mother," was published in 1948 in Astounding Magazine, and later that year she married her second husband, Frederick Pohl. By 1950 Merril's first novel, Shadow On the Hearth was published, as was her first anthology, Shot in the Dark. Soon after, Merril gave birth to her second daughter, Ann, and separated from Frederick a year later. Her second novel, written with Cyril Kornbluth, called Mars Child, and laterMars Output, was published in 1951; another of Merril's novels, The Tomorrow People, was published in 1963 ("Time Chronology").

For the second part of her career, Merril became a much sought after science fiction editor, as well as author. For example, from 1965-1969 Merril served as the book review editor for the magazine Fantasy and Science Fiction, and in 1967 Merril lived in England and edited the anthology England Swings SF; her short story collection, Daughters of Earth, was published in 1969. In 1970, however, Merril moved to Canada with her daughter Ann to protest the U.S. invovlement in the Vietnam. There she became a professor for a course on Science Fiction at the University of Toronto, and wrote hundreds of hours worth of documentaries for SF related projects ("Time Chronology").

In addition to her career as an author and editor, though, Merril was very influential in the SF community, and contirbuted to many foundations and groups to promote SF and its appreciation in society. While still living in the United States, Merril helped to organize the first Milford Science Fiction Writers' Convention in 1956. In 1970, while living in Toronto, Merril donated her collection of science fiction literature to the Toronto Public Library. This collection was the founding of the Spaced Out Library, renamed the Merril Collection of Speculative Fiction and Fantasy in 1991. Also, for periods during the 1970s and 80s, Merril ran science fiction workshops and seminars at alternative high schools in her area ("Time Chronology"). Merril was a science fiction writer who was highly revered during her lifetime, and still today. Indeed, her colleagues and those who knew her remember Merril for her strength and contribution to contemporary science fiction. In 1992, fellow SF author J.G. Ballad called Merril "the strongest woman in a genre for the most part created by weak and timid men."