He returned to Ireland in about 1880 and worked as editor of the New Ross Standard, reporting on the infamous Shanbogh killing as well as helping to organise the defence of the two accused.

He emigrated to Australia in 1882 to avoid re-arrest and helped to organise the Australian tour of the Irish nationalist leaders John and William Redmond in 1883.

[1][2] In 1897 Mahon stood unsuccessfully for the state seat of North Coolgardie, and the following year he was appointed editor of the Kalgoorlie Sun, a salacious newspaper similar to John Norton's Truth, in which he regularly denounced the Forrest government for alleged corrupt practices.

In July 1910 he moved a resolution in the House of Representatives requesting the new king George V to omit from the Coronation Oath references offensive to Catholics.

He re-entered Parliament in the seat of Kalgoorlie; following the death of the incumbent, Charlie Frazer, a by-election was called, but at the close of nominations on 22 December 1913 Mahon was the sole candidate and was declared elected unopposed.

Mahon held that position until the Labor Party split in November 1916 over conscription and he resigned from Prime Minister Billy Hughes' cabinet.

He kept a low profile during the referendum debate, but in the last week of campaigning, an article claiming that he supported a Yes vote forced him to clarify his position.

[7] When the Labor Party returned to government in 1929, Mahon sought to have his expulsion motion rescinded, but there was little interest in the caucus to revisit the matter.

[6] In 2016, Labor MP Graham Perrett moved a private member's motion in Parliament to recognise that Mahon's expulsion was unjust and a misuse of power then invested by the House.

On returning to Australia in June 1922, Mahon expected to be appointed Consul General for Ireland, but the Civil War put an end to that.

[6] In August 1931, while in Sydney for a meeting of the board of the Catholic Church Property Insurance Co, Mahon fell ill, and on his return to Melbourne succumbed to the lung disease that had plagued him all his life.

Another ardent Irish nationalist, the Catholic Archbishop of Melbourne, Daniel Mannix, said of him, "The late Mr Hugh Mahon was [my] personal and honoured friend.