Educated in Toronto public schools he first entered the business world in real estate. From there he moved on to the Toronto Railway Company becoming the general manager in 1905. Fleming"s political career began as an Alderman 1886 to 1890.
In 1892 was elected mayor of Toronto.
He was reelected in 1896 and the next year as mayor. He resigned in 1897 to accept appointment as an assessment commissioner of Toronto and held that position until 1904.
In 1894 presided over the National Exhibition Convention at Montreal. Fleming was president in 1895 of the Dominion Prohibitory Alliance.
He strongly believed in the prohibition of liquor traffic.
Fleming resigned as Mayor in 1897 and ran for mayor again in 1923 against Mayor Charles A. Maguire and was defeated. As a businessman he was general manager of the Toronto and Niagara Power Company, general manager of the Toronto Electric Light Company and general manager of the Electrical Development Company of Ontario. He was also director of the Toronto Board of Trade.
He was also a member of the Orange Order in Canada. He was a member of the Toronto Harbor Commission in 1921.