Cathleen Mann was born in Newcastle upon Tyne, the second daughter to painters Harrington Mann and Florence Sabine Paisley. Her father taught her to paint, following which she attended Slade School of Fine Art in London. Mann's work was first exhibited at the Royal Academy in 1924 and she exhibited regularly across the UK and in Paris. During the Second World War she worked as an official war artist, painting portraits of allied commanders for American magazines. She also worked in costume design for film and poster design during the interwar period. Landscapes, cityscapes, and portraits were the main subjects of Mann's paintings. Certain portraits which she painted have a cinematic quality, reflecting her time in the film industry.