She was born in County Kerry, Ireland. Her Irish journalist father deserted her Scottish mother -- and then died -- while Cecily was still a child. The rest of the family moved to Edinburgh, Scotland, where she was educated. She trained as an actress, taking the name "Rebecca West" from one of Ibsen's plays. She became involved in the women's suffrage movement before the First World War, and worked as a journalist on Freewoman and the Clarion. She met Wells in 1913, and their affair lasted ten years. They had a son, Anthony, but Wells was already married (for the second time). West is also said to have had affairs with Charlie Chaplin and newspaper magnate Max Beaverbrook.
In 1930, she married a banker, Henry Maxwell Andrews, and they remained together until his death in 1968. Before and during the Second World War, West travelled widely, collecting material for books on travel and politics. She was present at the Nuremberg trials. Her later work as a writer and broadcaster reflected these experiences.