Leigh Brackett was born December 7, 1915 in Los Angeles, California, and grew up there. On December 31, 1946, at age 31, she married Edmond Hamilton in San Gabriel, California, and moved with him to Kinsman, Ohio. She died of cancer in 1978 in Lancaster, California.

Often referred to as the "Queen of Space Opera", Brackett also wrote planetary romance. Almost all of her planetary romances take place in the Leigh Brackett Solar System, which contains richly detailed fictional versions of the consensus Mars and Venus of science fiction from the 1930s to the 1950s. Mars appears as a marginally habitable desert world, populated by ancient, decadent and mostly humanoid races; Venus as a primitive, wet jungle planet, occupied by vigorous, primitive tribes and reptilian monsters. Brackett's Skaith combines elements of her other worlds with fantasy elements.

Brackett first published in her mid-20s; the science fiction story "Martian Quest" appeared in the February 1940 issue of Astounding Science Fiction. Her earliest years as a Writer (1940–42) were her most productive. Some of her stories have social themes, such as "The Citadel of Lost Ships" (1943), which considers the effects on the native cultures of alien worlds of Earth's expanding trade empire.

Brackett's first novel, No Good from a Corpse (1944), was a hard-boiled mystery novel in the tradition of Raymond Chandler (The book resulted in her getting her first big screenwriting assignment.) After this, Brackett's science fiction stories became more ambitious. Shadow Over Mars (1944) was her first novel-length science fiction story; though somewhat rough-edged, it marked the beginning of a new style. This was strongly influenced by the characterization of the 1940s detective story and film noir.

Shortly after Brackett broke into science fiction writing, she wrote her first screenplays. Hollywood Director Howard Hawks was so impressed by her novel No Good from a Corpse that he had his secretary call in "this guy Brackett" to help william Faulkner write the script for The Big Sleep (1946). The film was written by Brackett, william Faulkner and Jules Furthman, and starred Humphrey Bogart. It is considered one of the best movies ever made in the genre.

Brackett returned to science fiction writing after her movie work, in 1948. From then on to 1951, she produced a series of science fiction adventure stories that were longer than her previous work, including such classic representations of her planetary settings as "The Moon that Vanished" and the novel Sea-Kings of Mars (1949). The latter was later published as The Sword of Rhiannon, a vivid description of Mars before its oceans evaporated.

In "Queen of the Martian Catacombs" (1949), Brackett created the character of Eric John Stark. Stark, an orphan from Earth, is raised by the semi-sentient aboriginals of Mercury, who are later killed by Earthmen. He is saved by a Terran official, who adopts Stark and becomes his mentor. When threatened, Stark reverts to the primitive N'Chaka, the "man without a tribe", who he was on Mercury. From 1949 to 1951, Brackett featured Stark (whose name echoes that of the hero in "Lorelei of the Red Mist") in three stories published in Planet Stories: "Queen of the Martian Catacombs", "Enchantress of Venus", and "Black Amazon of Mars". With this last story, Brackett's high adventure period of writing ended.

After getting married, Brackett took a long break from screenwriting. When she returned to screenwriting in the mid-1950s, she wrote for TV and movies. Howard Hawks hired her to write or co-write several John Wayne pictures, including Rio Bravo (1959), Hatari! (1962), El Dorado (1966), and Rio Lobo (1970). Because of her background with The Big Sleep, she later adapted Raymond Chandler's novel The Long Goodbye for the screen.

After 1955, Brackett concentrated writing for the more lucrative film and television markets. In 1963 and 1964, she briefly returned to her old Martian milieu with a pair of stories. "The Road to Sinharat" can be regarded as an affectionate farewell to the world of "Queen of the Martian Catacombs", and the other – with the intentionally ridiculous title of "Purple Priestess of the Mad Moon" – borders on parody.

Brackett and her husband shared Guest of Honor duties at the 22nd World Science Fiction Convention in 1965 in Oakland, California.

After another hiatus of nearly a decade, Brackett returned to science fiction in the 1970s with the publication of The Ginger Star (1974), The Hounds of Skaith (1974) and The Reavers of Skaith (1976), collected as The Book of Skaith in 1976. This trilogy brought Eric John Stark back for adventures upon the extra-solar planet of Skaith (rather than his old haunts of Mars and Venus).

Brackett worked on the screenplay for The Empire Strikes Back, the first Star Wars sequel. The film won the Hugo Award in 1981. This script was a departure for Brackett, as until then, all of her science fiction had been in the form of novels and short stories. Brackett's role in writing the script is disputed. George Lucas said that he asked Brackett to write the screenplay based on his story outline. Brackett wrote a finished first draft, which was delivered to Lucas shortly before her death from cancer on March 18, 1978. Two drafts of a new screenplay were written by Lucas and, following the delivery of the screenplay for Raiders of the Lost Ark, turned over to Lawrence Kasdan for a new approach. Both Brackett and Kasdan (though not Lucas) were given credit for the final script.

Laurent Bouzereau, in Star Wars: The Annotated Screenplays, said that Lucas disliked the direction of Brackett's screenplay, discarded it, and produced two more screenplays before turning the results over to Kasdan. Some fans, however, believe that they can detect traces of Brackett's influence in the dialogue and the treatment of the space opera genre in Empire. io9's co-founder Charlie Jane Anders has written that while "It's fashionable to disparage Brackett's contributions to Empire", "it's not true that none of Brackett's storyline winds up in the final movie — the basic story beats are the same."