Macdonald, John Sandfield, 1812–72, Canadian political leader. He was elected (1841) as a Conservative to the Legislative Assembly, but he afterward developed considerable political independence. He was solicitor general for Upper Canada (1849–51), speaker of the Legislative Assembly (1852–54), and attorney general for Upper Canada (1858). He was prime minister from 1862 to 1864. Although he was loyal to confederation after it was effected (1867), he had previously opposed it. He was chosen first prime minister of Ontario in 1867, but in 1871 he resigned when his coalition party was defeated by the Liberals.
See biography by B. W. Hodgins (1971).