De Camp was born in New York City, one of three sons of Lyon de Camp and Emma Beatrice Sprague. His maternal grandfather was the accountant, banker, pioneering Volapükist and Civil War veteran Charles Ezra Sprague.
Trained as an aeronautical engineer, De Camp received a Bachelor of Science degree in Aeronautical Engineering from the California Institute of Technology in 1930 and Master of Science degree in Engineering from Stevens Institute of Technology in 1933. He was also a surveyor and patent expert.
In 1939, he married Catherine Crook, with whom he collaborated on numerous works of fiction and nonfiction, beginning in the 1960s.
During World War II, de Camp worked at the Philadelphia Naval Yard with fellow authors Isaac Asimov and Robert A. Heinlein. He rose to the rank of Lieutenant Commander in the Naval Reserve.
He was a member of the all-male literary banqueting club the Trap Door Spiders, which served as the basis of Isaac Asimov's fictional group of mystery solvers the "Black Widowers". De Camp himself was the model for the Geoffrey Avalon character.
He was also a member of the Swordsmen and Sorcerers' Guild of America , 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.
The de Camps moved to Plano, Texas, in 1989. De Camp died there on November 6, 2000, seven months after the death of his wife of 60 years. He died on what would have been her birthday, just three weeks shy of his own 93rd birthday. His ashes were inurned with those of his wife in Arlington National Cemetery.
De Camp's personal library of about 1,200 books was acquired for auction by Half Price Books in 2005. The collection included books inscribed by fellow writers, such as Isaac Asimov and Carl Sagan, as well as de Camp himself.
De Camp was a materialist who wrote works examining society, history, technology and myth. He published numerous short stories, novels, non-fiction works and poems during his long career.
De Camp had the mind of an educator, and a common theme in many of his works is a corrective impulse regarding similar previous works by other authors. A highly rational and logical thinker, he was frequently disturbed by what he regarded as logical lapses and absurdities in others' writings. Thus, his response to Mark Twain's A Connecticut Yankee in King Arthur's Court was to write a similar time travel novel in which the method of time travel was rationalized and the hero's technical expertise both set at a believable level and constrained by the technological limitations of the age.
In like fashion, he reimagined space opera and planetary romances in his "Viagens Interplanetarias" series, and the prehistoric precursor civilizations characteristic of much heroic fantasy in his "Pusadian series". When he was not debunking literary conventions he was often explaining them, as with the early "Harold Shea", stories co-written with Fletcher Pratt, in which the magical premises behind a number of bodies of myths and legends were accepted as a given but examined and elucidated in terms of their own systems of inherent logic. De Camp's explanatory tendency also carried over into his non-fictional writings.
Science fiction
De Camp's science fiction is marked by a concern for linguistics and historical forces. His first published story was "The Isolinguals", in the September 1937 issue of Astounding Science Fiction. His most highly regarded works in the genre are his time travel and alternate history stories, including Lest Darkness Fall (1939), "The Wheels of If" (1940), "A Gun for Dinosaur" (1956), "Aristotle and the Gun" (1958), and The Glory That Was (1960) — in the last of which the "time travel" actually turns out to be a tour de force of historical recreation.
His most extended work was his "Viagens Interplanetarias" series, set in a future where Brazil is the dominant power, particularly a subseries of sword and planet novels set on the planet Krishna, beginning with The Queen of Zamba. His most influential Viagens novel was the non-Krishna work Rogue Queen, a tale of a hive society undermined by interstellar contact, which was one of the earliest science fiction novels to deal with sexual themes.
De Camp wrote a number of lesser-known but nonetheless significant works that explored such topics as racism, which he considered to be more accurately described as ethnocentrism. He pointed out that no scholar comparing the merits of various ethnicities has ever sought to prove that his own ethnicity was inferior to others.
Fantasy
De Camp was best known for his light fantasy, particularly the "Harold Shea" series and "Gavagan's Bar" series, both written in collaboration with his longtime friend Fletcher Pratt. The pair also wrote a number of stand-alone novels similar in tone to the Harold Shea stories, of which the most highly regarded is Land of Unreason. De Camp also produced a few more of this genre on his own.
He was also known for his sword and sorcery, a fantasy genre he was instrumental in reviving through his editorial work on and continuation of Robert E. Howard's "Conan" cycle. He himself wrote three sword and sorcery sequences of note. The early "Pusadian series", composed of the novel The Tritonian Ring and several short stories, are set in an antediluvian era similar to Howard's.
More substantial is the later "Novarian series", of which the core is the Reluctant King trilogy, beginning with The Goblin Tower, de Camp's most accomplished effort in the genre. The trilogy features the adventurer Jorian, ex-king of Xylar. Jorian's world is an alternate reality to which our own serves as an afterlife. Other novels in the sequence include The Fallible Fiend, a satire told from the point of view of a demon, and The Honorable Barbarian, a follow-up to the trilogy featuring Jorian's brother as the hero.
A late third series, composed of The Incorporated Knight and The Pixilated Peeress, is set in the medieval era of another alternate world sharing the geography of our own, but in which a Neapolitan empire filled the role of Rome and no universal religion like Christianity ever arose, leaving its nations split among competing pagan sects. The setting is borrowed in part from Mandeville's Travels.
Historical fiction
De Camp also wrote historical fiction, set in the era of classical antiquity from the height of the Persian Empire to the waning of the Hellenistic period, which forms a loosely-connected series based on their common setting and occasional cross references. They were also linked by a common focus on the advancement of scientific knowledge, de Camp's chosen protagonists being explorers, artisans, engineers, innovators and practical philosophers rather than famous names from antiquity, who are relegated to secondary roles. The best known of his historical novels is The Dragon of the Ishtar Gate.
Nonfiction
De Camp enjoyed debunking doubtful history and pseudoscientific claims of the supernatural, and explaining how ancient civilizations produced structures and architecture thought by some to be beyond the technologies of their time, such as the Pyramids of Ancient Egypt. Works in this area include Lost Continents, Citadels of Mystery, and The Ancient Engineers.
Among his many other wide-ranging non-fiction works were The Great Monkey Trial (about the Scopes Trial), The Ragged Edge of Science, Energy and Power, The Heroic Age of American Invention, The Day of the Dinosaur (which argued, among other things, that evolution took hold after Darwin because of the Victorian interest spurred by recently popularized dinosaur remains, corresponding to legends of dragons), and The Evolution of Naval Weapons (a United States of America government textbook).
The author also wrote pioneering biographies of many key fantasy writers, most as short articles, but two as full-length studies of the prominent authors Robert E. Howard and H. P. Lovecraft. The latter was the first major independent biography of the famous horror writer. De Camp's "warts and all" approach to his subjects has been branded by some fans as unflattering and unbalanced. For instance, Mark Finn, author of Blood and Thunder: The Life & Art of Robert E. Howard, contends that de Camp deliberately framed his questions in regard to Howard to elicit answers matching his Freudian theories about him.
