He was elected in a 1918 by-election held after the death of Robert Roswell Gamey, becoming the first member of his party to sit in the provincial assembly. He was re-elected in the 1919 provincial election in which the UFO staged an upset victory to form a coalition government with Independent Labour MLAs. Bowman was Minister of Lands and Forests in the provincial cabinet from 1920 to 1923.
He broke with the majority of UFO MLAs in Ontario following the 1923 provincial election when what had become known as the Progressive Party chose non-farmer William Edgar Raney as its leader. Instead, he and two other UFO MLAs sat as their own rump caucus, apart from the Progressives.
Bowman left provincial politics in 1926 to enter federal politics and was elected as a UFO MP for Algoma East to the House of Commons of Canada. In the 1930 federal election, he ran unsuccessfully for re-election as a Liberal candidate in 1930.