Dorothy "Diana" Knowles was born to a British family in Johannesburg, South Africa, where her father was working as a mining engineer. After he died when she was a small child, she was taken to England by her mother. The outbreak of World War I prevented them from returning to South Africa, so she attended a convent school and then Leeds University, where she graduated in 1928 with a bachelor's degree in French, followed by postgraduate study at the Sorbonne in Paris. Her research there became the basis of her first two books, La Réaction Idéaliste au Théâtre depuis 1890 (1934) and The Censor, the Drama and the Film (1934). Another well-known book was French Drama of the Inter-war Years 1918-39 (1967), which became a classic and remains essential reading for students of French theater. During the 1950s, she wrote about avant-garde theater, including Theatre of the Absurd, and was a popular guest lecturer at universities throughout the UK. In 1934, she began teaching at Liverpool University, where she remained for more than 30 years. After her retirement, she continued to teach and supervise postgraduate students as an Honorary Research Fellow at Bedford College, University of London. She was also a champion amateur fencer, a sport she continued into her 70s.