West was the daughter of an army officer and was educated in Edinburgh after her father's death in 1902. She later trained in London as an actress (taking her pseudonym from a role that she had played in Henrik Ibsen's play Rosmersholm).

From 1911 West became involved in journalism, contributing frequently to the left-wing press and making a name for herself as a fighter for woman suffrage. In 1916 she published a critical biography of Henry James that revealed something of her lively intellectual curiosity, and she then embarked on a career as a novelist with an outstanding—and Jamesian—novel, The Return of the Soldier (1918). Describing the return of a shell-shocked soldier from World War I, the novel subtly explores questions of gender and class, identity and memory. Her other novels include The Judge (1922), Harriet Hume (1929), The Thinking Reed (1936), The Fountain Overflows (1957), and The Birds Fall Down (1966). In 1937 West visited Yugoslavia and later wrote Black Lamb and Grey Falcon, 2 vol. (1942), an examination of Balkan politics, culture, and history. In 1946 she reported on the trial for treason of William Joyce (Joyce, William) (“Lord Haw-Haw”) for The New Yorker magazine. Published as The Meaning of Treason (1949; rev. ed., 1965), it examined not only the traitor's role in modern society but also that of the intellectual and of the scientist. Later she published a similar collection, The New Meaning of Treason (1964). Her brilliant reports on the Nürnberg trials were collected in A Train of Powder (1955). West was created a Dame Commander of the Order of the British Empire in 1959. During West's lifetime, her novels attracted much less attention than did her social and cultural writings, but, at the end of the 20th century, feminist critics argued persuasively that her fiction was formally as inventive as that of her female modernist contemporaries.

Rebecca West: A Celebration, a selection of her works, was published in 1977, and her personal reflection on the turn of the 20th century, 1900, was published in 1982. Selected Letters of Rebecca West, edited by Bonnie Kime Scott, was published in 2000. The critic and author Anthony West was the son of Dame Rebecca and the English novelist H.G. Wells (Wells, H.G.).