His mother, Henrietta Emma Rex, was an Australian who helped form the Women's Social and Political League and was vice-president in 1894.

He won a scholarship and attended Victoria University where graduated in 1907 with a Master of Arts with honours in mathematics and a Bachelor of Laws.

He finally won Eden in a 1926 by-election, assisted by the fact that the Reform Party's vote was split by a defeated nominee, Ellen Melville.

Mason was regarded as a social democrat rather than a socialist, and he played a part in moving the Labour Party closer to the political centre.

He did, however, believe that the state should have exclusive control over the country's financial system, influenced by social credit monetary reform theories.

Other causes supported by Mason include the establishment of a comprehensive old-age pension system and the granting of full state services to naturalised immigrants (the latter making him extremely popular with his electorate's substantial Yugoslavian community).

In 1941 the Public Service Commissioner Thomas Mark died in (or just outside) the minister's office, during a confrontation with Mason who wanted the resignation of the head of a department.

In 1953 Mason was among several Labour MPs who attempted an abortive coup to remove the 71-year-old Walter Nash as party leader, others included Bill Anderton and Arnold Nordmeyer.

[11] In 1959 he introduced a bill proposing that men convicted of homosexual acts should be dealt with as merely indecent assaults and therefore carry a lighter penalty.

In 1961 Nationals deputy leader Jack Marshall retracted much of his party's criticism, claiming they had misunderstood the intention of the bill.

[12] Mason eventually retired from politics at the 1966 election, under a certain amount of pressure from colleagues who wished to "rejuvenate" the Labour Party.