was a lawyer and political figure in Ontario, Canada. He represented Lambton West in the Legislative Assembly of Ontario from 1902 to 1919 as a Conservative member.
Hanna served as Acting Premier of Ontario from 25 September 1914 to 2 October 1914, after the death of Sir James Whitney, before Sir William Hearst.
Hanna was unsuccessful in the federal elections of 1896 and 1900 before being elected to the provincial assembly in 1902. He served as Provincial Secretary and Registrar from 1905 to 1916. In 1915, Hanna initiated an overhaul of Ontario's prison systems by closing down facilities which treated prisoners harshly, and he took special interest in improving the operations of prisons in Ontario to be more humane. That legacy remains in Toronto's Liberty Village whose name comes from the neighbourhood's main road, Liberty Street, near the former site of Toronto's Central Prison, which was closed by Hanna.
In 1916, Hanna introduced the Ontario Temperance Act, which prohibited the sale of alcohol except for medicinal purposes or use in church services for the remainder of World War I. Hanna also served as an adviser to Prime Minister Robert Laird Borden. In 1917, he was named food controller for Canada, charged with dealing with food shortages and inflation near the end of the war. He resigned from his position in January 1918 due to poor health. However, he became president of Imperial Oil later that year.
Near the end of 1918, the Hanna family had been shaken by the death in Italy of his son, William Neil, a Royal Air Force lieutenant. Hanna went south for the winter to deal with the shock and his own failing health. While in Augusta, Georgia, he suffered a stroke and died. After a Methodist service, he was buried in Lakeview Cemetery in Sarnia.