Duncan McArthur (1885 – July 20, 1943) was an archivist, educator, civil servant and political figure in Ontario. He represented Simcoe Centre from 1940 to 1943 in theLegislative Assembly of Ontario as a Liberal.

Born in Dutton, Ontario, McArthur was educated in Dutton, at Queen's University and at Osgoode Hall. He worked at the Dominion Archives of Canada from 1907 to 1912. In 1915, he was called to the Ontario bar and practised law in Toronto for two years. From 1919 to 1922, he was assistant general manager for a trust company. In 1920, McArthur married Floy Lawson.In 1922, he joined the history department at Queen's University, later serving as department head. In 1934, he became Ontario's Deputy Minister of Education.

McArthur was elected to the Ontario assembly by acclamation in 1940 following the death of Leonard Simpson.He served in the Ontario cabinet as Minister of Education from 1940 to 1943.