Roger Joseph Zelazny was born in Euclid, Ohio, the only child of Polish immigrant Joseph Frank Żelazny and Irish-American Josephine Flora Sweet. In high school, he became the editor of the school newspaper and joined the Creative Writing Club. In the fall of 1955, he began attending Western Reserve University and graduated with a B.A. in English in 1959. He was accepted to Columbia University in New York and specialized in Elizabethan and Jacobean drama, graduating with an M.A. in 1962. His M.A. thesis was entitled Two traditions and Cyril Tourneur: an examination of morality and humor comedy conventions in The Revenger's Tragedy. Between 1962 and 1969 he worked for the U.S. Social Security Administration in Cleveland, Ohio and then in Baltimore, Maryland spending his evenings writing science fiction. He deliberately progressed from short-shorts to novelettes to novellas and finally to novel-length works by 1965. On May 1, 1969, he quit to become a full-time writer, and thereafter concentrated on writing novels in order to maintain his income. During this period, he was an active and vocal member of the Baltimore Science Fiction Society, whose members included writers Jack Chalker and Joe and Jack Haldeman among others.
Zelazny was married twice, first to Sharon Steberl in 1964 (divorced, no children), and then to Judith Alene Callahan in 1966 (he had also been engaged to folk singer Hedy West for six months in 1961/62). Roger and Judy had two sons, Devin and Trent (an author of crime fiction) and a daughter, Shannon. At the time of his death, Roger and Judy were separated and he was living with author Jane Lindskold.
His first fanzine appearance was part one of the story "Conditional Benefit" (Thurban 1 #3, 1953) and his first professional publication and sale was the fantasy short story "Mr. Fuller's Revolt" (Literary Calvalcade, 1954). As a professional writer, his debut works were the simultaneous publication of "Passion Play" (Amazing, August 1962) and "Horseman!" (Fantastic, August 1962). "Passion Play" was written and sold first. His first story to attract major attention was "A Rose for Ecclesiastes", published in The Magazine of Fantasy and Science Fiction, with cover art by Hannes Bok.
Roger Zelazny was also a member of the Swordsmen and Sorcerers' Guild of America (SAGA), a loose-knit group of heroic fantasy authors founded in the 1960s, some of whose works were anthologized in Lin Carter's Flashing Swords! anthologies.
Raised as a Catholic by his parents, Zelazny later declared himself a lapsed Catholic and remained that way for the rest of his life. "I did have a strong Catholic background, but I am not a Catholic. Somewhere in the past, I believe I answered in the affirmative once for strange and complicated reasons. But I am not a member of any organized religion."