He was born in Richmond, Ontario, the son of Thomas Dunbar, and was educated in Kemptville. In 1892, he married a Miss Coxford. He served as a captain during World War I. Dunbar was controller for the city of Ottawa. He ran for mayor of Ottawa in 1938, but placed third. He served in the provincial cabinet as Minister of Municipal Affairs from 1943 to 1955 and Minister of Reform Institutions from 1946 to 1948; Dunbar was Provincial Secretary and Registrar of Ontario from 1943 to 1946 and from 1955 to 1958.