Born in Sewickley, Pennsylvania, Stewart was the son of a railway engineer. He earned a bachelor's degree from Princeton University in 1917, an MA from the University of California, Berkeley, and his Ph.D. in English literature from Columbia University in 1922. He accepted a position in the English department at Berkeley in 1923.

Stewart was a founding member of the American Name Society in 1956-57, and he once served as an expert witness in a murder trial as a specialist in family names. His best-known academic work is Names on the Land: A Historical Account of Place-Naming in the United States (1945; reprinted, New York Review Books, 2008). He wrote three other books on place-names, A Concise Dictionary of American Place-Names (1970), Names on the Globe (1975), and American Given Names (1979). His scholarly works on the poetic meter of ballads (published under the name George R. Stewart, Jr.), beginning with his 1922 Ph.D. dissertation at Columbia, remain important in their field.

He is best known for his only science fiction novel Earth Abides (1949), a post-apocalyptic novel, for which he won the first International Fantasy Award in 1951. It was dramatized on radio's Escape and served as an inspiration for Stephen King's The Stand, as King has stated.

His 1941 novel Storm, featuring as its protagonist a Pacific storm called "Maria," prompted the National Weather Service to use personal names to designate storms and inspired Alan Jay Lerner and Frederick Loewe to write the song "They Call the Wind Maria" for their 1951 musical Paint Your Wagon. Storm was dramatized as A Storm Called Maria on a 1959 episode of ABC's Disneyland. Two other novels, Ordeal by Hunger (1936) and Fire (1948) also evoked environmental catastrophes.

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• Bret Harte: Argonaut and Exile (1931)
• Ordeal by Hunger: The Story of the Donner Party (1936; rpt. 1992). ISBN 978-0395611593
• John Phoenix (1937)
• East of Giants (1939)
• Doctor's Oral (1939)
• Take your Bible in one hand;: The life of William Henry Thomes, author of A whaleman's adventures on land and sea, Lewey and I, The bushrangers, A gold hunter's adventures, etc.", 1939
• Storm (1941; rpt. 2003). ISBN 978-1890771744
• Names on the Land: an historical account of place-naming in the United States (1945; rpt. 2008). ISBN 978-1590172735
• Man, An Autobiography (1946)
• Fire (1948)
• Earth Abides (1949; rpt. 2006). ISBN 978-0345487131
• The Year of the Oath (in collaboration) (1950)
• Sheep Rock (1951)
• The Opening of the California Trail: the story of the Stevens party by Moses Schallenberger, 1888; edited 1953
• U.S. 40: Cross Section of the United States of America (1953)
• American Ways of Life (1954)
• To California by Covered Wagon (1954)

reprinted as Pioneers Go West (1987)

• The Years of the City (1955)
• N.A. 1: The North-South Continental Highway (1957)
• Pickett's Charge (1959)
• The California Trail (1962)
• Pickett's charge: A microhistory of the final attack at Gettysburg, July 3, 1863 (Premier Civil War Classic), 1963
• Committee of Vigilance (1964)
• Good Lives (1967)
• Not So Rich as You Think (1968)
• A Concise Dictionary of American Place-Names (1970)
• Names on the Globe (1975)
• American Given Names (1979). ISBN 978-0195040406