He later joined Western Australian Government Railways,[3] and in 1937 was working as a shunter at York in which capacity he testified before an arbitration tribunal.

[4] He later worked as a guard based at West Midland and was active in the Amalgamated Society of Railway Employees, serving on the state executive.

[5] In January 1943, Mountjoy won ALP preselection for the Division of Swan, at which time he was secretary of the party's Midland district council.

[10] In November 1946, months after his parliamentary defeat, Mountjoy was appointed by the Chifley government to a three-year term on the executive of the Council for Scientific and Industrial Research (CSIR).

[11] His appointment was criticised by the opposition on the grounds that he was not academically qualified, was closely affiliated with the Communist Party, and that the position had not been offered to a returned soldier.