Yvonne Kapp, née Mayer, was born in London to a middle-class German-Jewish family. She went to work at the age of 18. In 1922, she married Edmond Kapp, an artist and musician considerably older than herself, with whom she had a daughter. They lived the life of bohemians of the 1920s, moving between an apartment in London and the houses of friends in England, the Italian Riviera, and Capri. Yvonne supported the family with her freelance journalism, and worked in 1927 as the literary editor of Paris Vogue. In addition to a number of nonfiction works, she also published four novels under the name of Yvonne Cloud, including Nobody Asked You (1932) and By The Houses In Between (1938). She became a Communist in 1936, following the rise of the Nazi regime in Germany, and worked with German and Spanish refugees in the UK. In 1938, she was appointed Assistant to the Director of the British Committee for Refugees from Czechoslovakia. She became a speechwriter for Jack Tanner, president of the Amalgamated Engineering Union (AEU), and then worked as an editor and translator. Her translations include works by Ilya Ehrenburg, Paul Lechat, and Bertolt Brecht. She learned about Eleanor Marx while working on some correspondence between Frederick Engels and Laura Lafargue. Her two-volume work entitled Eleanor Marx (1972 and 1976), 10 years in the making, is considered a masterpiece of 20th-century biography.