Piddington was sympathetic to the labour movement, and in April 1913 Andrew Fisher nominated him to the High Court as part of a court-packing attempt.

His father was born in England and arrived in the colony of Tasmania as a young man, where he was a Methodist lay preacher.

[2] His father eventually joined the Church of England and served as an ordained minister in various towns in country New South Wales, ending his career as an archdeacon at Tamworth.

[1] After graduating from university, Piddington taught Latin and Greek for a period at the newly created Sydney High School.

[2] He subsequently read for the bar and was admitted as a barrister in 1890, serving as a judge's associate under William Windeyer for a period.

[3] Piddington first stood for parliament at the 1894 New South Wales general election, running on a radical platform against incumbent premier George Dibbs.

Piddington reprised his candidacy against Dibbs in Tamworth and was narrowly elected as a Free Trader, in what was regarded as a "highlight of the Reidites' triumph".

[3] With his parliamentary term beginning on 24 July 1895,[4] Piddington was subsequently chosen by Reid to move the address-in-reply in the first session of the new parliament.

[6] According to his biographer Michael Roe, "his ideas were akin to Labor but membership of any party probably repelled him; he grasped Reid's good points, but the personality gap between himself and that dominating figure of the day was immense".

In this context, Fisher and Hughes were looking for justices who would have a broad interpretation of the Constitution of Australia, particularly of Section 51, which divides powers between the federal and state governments.

Hughes, who had been widely criticised for trying to stack the court, labelled Piddington a coward after the incident, and called him a "panic-stricken boy".

[11] Piddington was one of six justices of the High Court to have served in the Parliament of New South Wales, along with Edmund Barton, Richard O'Connor, Adrian Knox, Edward McTiernan and H. V. Evatt.

In September 1913, Piddington was appointed as the chairman of the Interstate Commission by Joseph Cook, the new Commonwealth Liberal Party Prime Minister.

He held that position until 1932, when following Governor of New South Wales Sir Philip Game's dismissal of the Lang government, Piddington resigned in protest, despite being just a few weeks short of being entitled to a pension.

[14] In 1934, Piddington was engaged by Czechoslovak writer Egon Kisch to represent him in his cases against the Australian government, which sought to deport him for his left-wing political views.

[16] Following Evatt's ruling, the government then attempted to secure Kisch's deportation by administering him a dictation test in Scottish Gaelic under the Immigration Restriction Act 1901.