Moss was born to a Jewish family in Dunedin, New Zealand, where his father, formerly resident in Victoria, was a music teacher and choirmaster.

However, the sitting member, William Pearse, resigned his seat the following year to travel to England, and Moss was elected at the resulting by-election.

[6] When first Leake government fell in November 1901, Alf Morgans nominated Moss to fill the role of Colonial Secretary in his new ministry.

[3] Moss's time out of parliament was short, however – he nominated for the vacancy in West Province left by the retirement of Alfred Kidson, and was elected uncontested, being sworn in in May 1902.

[7] George Leake died in June 1902, and Moss was back in favour in the new ministry led by Walter James, becoming (along with John Nanson) a minister without portfolio.

This situation persisted until the defeat of James's government in parliament after the 1904 state election, after which Henry Daglish was sworn in as Western Australia's first Labour Party premier.

Following the result of the 1933 secession referendum, Moss, a longtime advocate of the withdrawal of Western Australia from the Commonwealth, was made one of four members of the unsuccessful delegation to the British government, along with Sir Hal Colebatch, James MacCallum Smith, and Keith Watson.