Cowan served as a councillor on the
District Council of Mobilong from 1892 to 1912 including the role of chairman from 1896 to 1912. He was elected to the Legislative Council district of the Southern District on 2 April 1910 and held this seat until his retirement on 29 February 1944. Cowan served as the Minister of Agriculture, the Assistant Minister of Repatriation and the Minister of Town Planning in the government led by
Henry Barwell and as the Minister of Agriculture, the Minister of Immigration, the Minister of Repatriation, and the Minister of Irrigation in the government led by
Richard Layton Butler. He also served as the
Government Whip in the Legislative Council for a period of 20 years and as a member of the Parliamentary Standing Committee on Public Works from 12 July 1934 to 31 May 1944. ==Later life and death==