[1] McNish was born in Blantyre, South Lanarkshire, Scotland in 1895 where his father was a headmaster.
He joined the Canadian Expeditionary Force during World War I where he served with the Canadian Military Engineers for four years in Europe and was awarded the Military Medal for bravery.
He first stood for the Board of Control in the December 1936 Toronto municipal election but was defeated.
He won a seat on the Board of Control in the 1937 Toronto municipal election and was re-elected in 1939 and 1940. in the 1941 Toronto municipal election he and fellow Controller Frederick J. Conboy both ran for mayor with Conboy winning 55,677 votes to McNish's 33,024.
He retired from politics, serving as a magistrate before returning to his law practice until 1979 when he suffered a stroke.