On 2 June 1930, he married Irma Priest at St Andrews' Church in Subiaco, with whom he was to have two sons and three daughters.
In the 1930s, he worked as a labourer and storeman, and became a foreman of sustenance gangs during the Great Depression who were digging contoured channels on dams in the South West region.
He signed up for the Royal Australian Air Force in 1941, but was rejected on medical grounds and was officially discharged on 9 February 1942.
The previous Liberal member, Les Nimmo, had decided to contest the seat of Leederville, and Marshall's strongest support came from his own suburb, where he obtained 66% of the vote.
He resigned from his job at the State Electricity Commission and completed a term as a government backbencher.