Knowles was born Lilian Tomm in Truro, Cornwall in 1870, and died in London on 25 April 1926. She was educated at Truro High School and then at Girton College, Cambridge, where she received first-class results in both the history tripos in 1893 and part I of the law tripos in 1894. Her interest in economic history was stimulated by hearing the lectures of William cunningham. In 1895 she became one of the first research students at the newly-opened London School of Economics, remaining there until 1899. In 1904 she was appointed a permanent lecturer in economic history at the LSE; she was made a reader in 1907. In 1920–24 she was dean of the Faculty of Economics at the University of London. In 1921 she was appointed professor of economic history at the LSE, the first person to hold that post, She married C.J. Knowles, a barrister, in 1904; they had one son.
From The Biographical Dictionary of British Economists in Oxford Reference.