Garson was first elected to the Legislative Assembly of Manitoba for the riding of Fairford in 1927 as a Progressive, defeating incumbent Liberal Albert Kirvan.

Garson's ministry began a program of rapid rural electrification, and made some effort to service the needs of returning soldiers after World War II.

All the same, he rejected demands from the Manitoba Co-operative Commonwealth Federation to introduce programs in public housing and old-age pensions.

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 for the rural seat of Marquette the next month.

Garson lost his seat in 1957, the year that Progressive Conservative leader John Diefenbaker formed a minority government.