Frank Hawkins Underhill, OC FRSC (November 26, 1889 – September 16, 1971) was a Canadian journalist, essayist, historian, social critic and political thinker.
Frank Underhill, born in Stouffville, Ontario, was educated at the University of Toronto and the University of Oxford where he was a member of the Fabian Society. He was influenced by social and political critics such as Bernard Shaw and Goldwin Smith. He taught history at the University of Saskatchewan from 1914 until 1927 with a long interruption during World War I during which he served as an officer in the Hertfordshire Regiment of the British Army on the Western Front. He also taught from 1927 until 1955 at the University of Toronto. He left the University of Toronto due to a dispute with the administration and later joined the faculty at Carleton University.
During the Great Depression, Underhill joined several other left wing academics in forming the League for Social Reconstruction. He was also a founder of the Co-operative Commonwealth Federation and helped write its Regina Manifesto in 1933. He joined the editorial staff of the leftist Canadian Forum in 1927 where he wrote a column of political commentary called "O Canada" from 1929 on and served for a time as chair of that journal's editorial board. Despite these progressive leanings, Underhill had a conservative view of the historical profession and impeded the careers of several women historians.