Catharines, Ontario, Garson was first elected to the Legislative Assembly of Manitoba for the riding of Fairford in 1927, defeating incumbent Liberal Albert Kirvan.
Garson was sworn in as provincial Treasurer on September 21, 1936.
On November 15, 1948, Garson was sworn in as Minister of Justice and Attorney General; he was elected to the federal parliament in a by-election the next month.