Rosamond Nina Lehmann was born in Bourne End, Buckinghamshire, as the second daughter of Rudolph Lehmann and his wife Alice Davis, a New Englander. Her father Rudolph Chambers Lehmann was a liberal MP, and editor of the Daily News. John Lehmann (1907-1989) was her brother; one of her two sisters was the famous actress .

In 1919 she went to Girton College, University of Cambridge to read English Literature, an unusual thing for a woman to do at that time. In December 1923 she married Leslie Runciman (later 2nd Viscount Runciman of Doxford) (1900-1989), and the couple went to live in Newcastle upon Tyne. It was an unhappy marriage, and they separated in 1927 and were divorced later that year.

In 1927, Lehmann published her first novel, Dusty Answer, to great critical and popular acclaim. The novels heroine, Judith, is attracted to both men and women, and interacts with fairly openly gay and lesbian characters during her years at Cambridge. The novel was a succès de scandale. Though none of her later novels were as successful as her first, Lehmann went on to publish six more novels, a play (No More Music, 1939), a collection of short stories (The Gypsys Baby & Other Stories, 1946), a spiritual autobiography (The Swan in the Evening, 1967), and a photographic memoir of her friends (Rosamond Lehmanns Album, 1985), many of whom were famous Bloomsbury figures such as Leonard and Virginia Woolf, Carrington, and Lytton Strachey. She also translated two French novels into English: Jacques Lemarchands Genevieve (1948) and Jean Cocteaus Children of the Game (1955). Her novels include A Note in Music (1930), Invitation to the Waltz (1932), The Weather in the Streets (1936), The Ballad and the Source (1944), The Echoing Grove (1953), and A Sea-Grape Tree (1976).

In 1928, Lehmann married Wogan Philipps, an artist. They had two children, a son Hugo (1929-1999) and a daughter Sarah or Sally (1934-1958), but the marriage quickly fell apart during the late Th