Patrick Joseph O'Regan was born in New Zealand on 6 February 1869 at Charleston, on the West Coast, the son of Irish immigrants Patrick O'Regan, a goldminer, and his wife, Mary Burke. Three years later he and his family moved inland to Inangahua Junction, where his father became a farmer and part-time road contractor. Largely self-taught, young Patrick did not go to school until 1883, when he spent less than a year at Father Rolland's academy at Ahaura. Bush-felling, fencing, milking, pit-sawing and carpentry were his daily occupations. Any spare hours were spent reading whatever came to hand, principally Irish nationalist books and newspapers.
Despite his limited formal education, O'Regan frequently contributed to the local press on labour issues (under the pseudonym 'Horny Hand'). In 1891 he accepted an offer to edit the Reefton Guardian, moving on soon afterwards to the Inangahua Times. The step from journalism to politics was a natural one. He gave Robert Stout a scare in the Inangahua by-election held in June 1893, before taking the seat at the general election later in the same year (Stout having moved on to contest City of Wellington). At 24 O'Regan became the youngest member of the House of Representatives. Three years later he was elected for Buller.
Patrick O'Regan's fluency and passionate commitment made an immediate impression on his new audience. He was loosely associated with the Liberal government, but was happiest when in opposition. Truculently independent, throughout his career he relished championing minority causes such as electoral reform and land value taxation. After discovering the writings of Henry George in 1890, O'Regan became a tireless and uncompromising advocate of the single tax. In 1896 he helped pass legislation providing for rating on the unimproved value of land. He also introduced three bills in favour of proportional representation, managing to coax the 1899 measure past its second reading.
O'Regan was disappointed by the inevitable compromises of political life. He attributed his electoral defeat in 1899 to the party-machine politicians' dislike of his independent line and of his Roman Catholicism. He failed at the polls again in 1902 and 1905.
On 21 May 1898 at Nelson he married Clara Emma Haycock, a schoolteacher. They were to have six children. In 1900 Patrick took his family to Wellington and commenced legal studies at Victoria College. Years of financial stringency and hard work were crowned in 1908 with his admission to the Bar.
O'Regan's practical experience and inclinations soon attracted a heavy case-load under the Workers' Compensation Act 1908 and earned him a solid reputation as a working-man's lawyer. Two of his cases reached the Privy Council and ended in notable victories. He acted as attorney for the New Zealand Federation of Miners (1908–9) and the New Zealand Federation of Labour (1909–13). His legal talents and radical views were enlisted in defence of various labour leaders before, during and after the First World War. O'Regan also helped to organise an escape route to Australia for those at risk of conscription under the Military Service Act 1916.
He took an increasingly prominent role in Catholic and Irish affairs, culminating in his presidency of the Irish Self-Determination League of New Zealand (1921) and in his successful defence of Bishop James Liston on a charge of sedition (1922). Opposition to conscription and support for Irish nationalism brought the Catholic church and the New Zealand Labour Party together, with O'Regan acting as a vital link. He wrote on radical issues in both the New Zealand Tablet and Maoriland Worker, and worked behind the scenes after the war to forge an informal Labour–Liberal–Catholic alliance against the dominant Reform Party. O'Regan's love for Ireland was matched by a deep pride in his native land. A fierce conservationist, he returned each year to holiday in Westland. His political energies were similarly directed towards the improvement of New Zealand conditions. When the Irish issue reached an imperfect solution with the conclusion of the Anglo-Irish Treaty of 1921, he expressed his relief in typically forthright terms: 'In one way I am pleased the rationale for the [Irish Self-Determination] League's existence is about to end for one reason that we have enough to do with our own affairs in this ass-ridden country'.
Preferment came very late in life for a man of his considerable talents. The Labour government appointed him a judge of the Court of Arbitration in 1937, and an MLC in 1946. He died in Wellington on 24 April 1947, survived by his wife, Clara, three sons and two daughters. Square-jawed and determined in appearance, O'Regan rose by talent and application. He held firm to his political and religious beliefs whatever temporal disadvantage this involved. Patrick O'Regan called no man master.