Joseph McMullen Dargaville, the son of Anderson Dargaville, a physician, and his wife, Eliza McMullen, was born in Cork, County Cork, Ireland, and baptised there on 27 June 1837. His paternal ancestors were Huguenots who had fled to Ireland to escape persecution. Joseph attended Fermoy College, an institution noted for its liberal education.
As a young man Joseph Dargaville emigrated with his brothers to Victoria, Australia. In February 1859 he moved to Sydney, where he was employed as a clerk by the Union Bank of Australia at a salary of £100 per annum. From 1860 to 1866 he worked in several branches of the bank in New South Wales, Tasmania and Victoria. By 1866 regular promotions and salary increments reflected the bank's confidence in his abilities. On 20 April 1865 at Portland, Victoria, Dargaville married Anne Must. The couple were to have at least six children.
In July 1867, probably because of his banking experience during the goldrush in Victoria, he was appointed inspector of the Union Bank's agencies on the West Coast of New Zealand at a salary of £500. The discovery of gold there in 1864 had brought a large increase in population. Dargaville arrived at Hokitika in August. He was promoted to acting manager of the Auckland branch in 1868, but a projected transfer to Nelson was evidently not acceptable and in July 1869 he resigned. He joined the Melbourne firm of Must and Company as their Auckland agent and opened a business as a wholesale merchant in Hobson's Buildings, Shortland Street.
In 1871 he visited the Northern Wairoa River on the northernmost arm of the Kaipara Harbour. Recognising the trade potential of the relatively undeveloped resources of kauri timber and gum, he leased from Parore Te Awha four acres on the adjacent Kaihu River. He set up a trading post and built up a prosperous timber industry that by 1876 was reputed to employ over 400 men. Dargaville commuted frequently from Auckland until late in 1871, when he promoted Edwin Mitchelson, a member of his staff, to local manager.
In 1872 Dargaville purchased from Parore and others the Tunatahi block of 171 acres, and at the junction of the Wairoa and Kaihu rivers founded and developed the town of Dargaville. At his own expense he built a large store and gum shed, and tramways and wharves to service the expanding overseas trade. In time, cottages and two hotels were erected and in 1874 a spacious family home was built on a prime site in the town. He donated land for the Anglican church and for a school and was one of the original promoters of the Kaihu valley railway connecting Kaihu with Dargaville.
In 1876 Joseph Dargaville sold part of his timber interests to the Union Sash and Door Company and Edwin Mitchelson took over his merchant businesses. Dargaville continued to own, almost exclusively, the land and buildings of the township, from which he derived considerable income through leasing. To gain the maximum economic advantage from his estate he established the Dargaville Trust and transferred the management of his property to the trustees.
As a resident of Auckland and a landowner in Dargaville he involved himself in local affairs and politics. Dargaville was a member of the Auckland City Council from 1872 to 1874 and represented Auckland East on the Auckland Provincial Council from 1873 to 1876. In 1873 he unsuccessfully contested the superintendency against John Williamson and H. H. Lusk. He stood again in 1875 but retired in favour of Sir George Grey. While a member of the Provincial Council he published a plea for a united colony when separation of the North and South islands was mooted. He was a member of the Hobson County Council from 1876 to 1890.
In 1881 he was elected to the House of Representatives for City of Auckland West as an independent. He was against New Zealand participation in a proposed confederation with Australia, and under the auspices of the Auckland Trades and Labour Council published a pamphlet to this effect. Dargaville was censured for a speech he gave in Parliament on 31 July 1883, in which he accused Premier Frederick Whitaker and Colonial Treasurer H. A. Atkinson of using their political position to promote legislation which was in the interests of private institutions and not for the good of the colony. Although the select committee appointed to inquire into the allegations said that the speech imputed 'political corruption against the Premier and Treasurer', Dargaville denied that this was his intention. On 4 September the committee found his charges to be unsubstantiated and dismissed them. Dargaville retired from the seat in July 1887 and stood again for Parliament, without success, in the next three elections.
He represented Parnell on the Auckland Harbour Board, was a member of the Auckland Education Board and Auckland College and Grammar School board, and was a justice of the peace. A prominent Freemason, he founded the Lodge of St George in 1878, and was grandmaster of the Orange Lodge of New Zealand. He held a captain's commission in the Auckland Engineer Volunteers and in the Dargaville Volunteers.
Joseph Dargaville was a shrewd businessman and a commanding figure with a dominant personality. It was due to his enterprise and business ability that a thriving kauri timber and gum industry, centred on Dargaville, was established. This industry made a significant contribution for many years to the struggling economy of the colony. He was a fluent speaker and debater in Parliament and on the hustings, but his forthright manner and strong opinions were not always acceptable to his colleagues and constituents.
Returning from a visit to England he died on board the Mariposa on 27 October 1896, and was buried at sea. In 1910 a stained glass window was installed in the Holy Trinity Church, Dargaville, in his memory. His wife, Anne, who was noted for her philanthropic activities, died on 5 July 1915.