James Williamson is said to have been born in 1814, in Belfast, Ireland, the son of Ann Gardiner and her husband, Thomas Williamson, a linen merchant and ship owner of that city.
While still a boy, James went to sea on one of his father's vessels. Later, as a ship's officer, he travelled widely. Early in 1840, after sailing as chief mate on a vessel from Sydney, New South Wales, to the Bay of Islands, New Zealand, he gave up the sea. On the beach at Kororareka (Russell) he opened a humble store, selling a few supplies to settlers and Maori, and rum to sailors.
The next year he moved to Auckland where he bought for £266 a quarter acre allotment at the foot of Shortland Crescent. He entered into partnership with Thomas Crummer. The firm ran a store in Shortland Crescent, and a public house, the Victoria Hotel, on the waterfront. Williamson and Crummer quickly prospered.
The greatest coup of the partners was acquiring, for a song, Surrey Hills, a suburban farm of 314 acres situated within a mile of Queen Street. Nine years after Crummer's death in 1858, Williamson bought out the interest of Crummer's sons for £11,000. When Auckland grew rapidly in the 1870s Surrey Hills estate skyrocketed in value, as a prime area for subdivision. To his chagrin, Williamson in old age found himself denounced as a land monopolist.
On 29 April 1857 Williamson married Julia Maria Seidler of London, England, a well-connected and polished young woman of 26, who, for her black hair, blue eyes, and delicate complexion, was considered one of the beauties of Auckland. Six children (three sons and three daughters) were the issue of this marriage.
Already a man of substance when war broke out in 1861, Williamson was further enriched by commissariat contracts. He also speculated profitably in city and suburban land and shrewdly invested in the Thames goldfields. He seemed the very epitome of the self-made merchant-prince. Such were the 'unlimited means at his command', surmised the Observer, 'he could, if he chose, almost recall the fable of Aladdin.'
Although Williamson was briefly (1862–67) a member of the House of Representatives, where he spoke little, and then of the Legislative Council (1870–88), his public service was in finance. He was one of the Auckland businessmen who founded the New Zealand Insurance Company (1859), the Bank of New Zealand (1861), and the New Zealand Loan and Mercantile Agency Company (1865). He served on their Auckland boards almost continuously until his death, arousing in his fellow directors admiration for his experience and judgement, and alarm at his occasional petulance and uncertain temper.
On 17 July 1877 Williamson bought from Thomas Russell for £10,000 a 313 acre estate near Onehunga, named Pah Farm, and set about building the most palatial gentleman's residence in Auckland, a two-storeyed Italianate mansion in plastered brick. The grounds were lavishly planted; even the stables and outbuildings were resplendent. There was a large retinue of servants: 'one could imagine oneself back in old England in an old county house', said a visitor in 1882. Understandably, locals called it 'Williamson's Castle'.
Yet within five years of its completion Williamson was on the brink of bankruptcy. He subdivided and sold off his Surrey Hills estate, but failed to retrieve his financial position. Williamson was undone not by Auckland's commercial recession in the 1880s but by the collapse of the market for provincial farmland. After the Waikato war Williamson had invested heavily in confiscated land. Much of it was swamp and required considerable expenditure before its great potential value could be realised.
Dwarfing all Williamson's other land speculations was the Auckland Agricultural Company, formed in 1881 to develop estates in the middle Waikato Valley and totalling 78,455 acres. The financial responsibility rested with four men: James Williamson, Thomas Russell, and the brothers Robert and Every Maclean. By November 1887 the company was insolvent, unable, in the midst of a deep rural depression, to meet interest repayments due to its chief mortgagee, the Bank of New Zealand.
Williamson was insolvent, too. During his last months of life he was frantic with worry. After his death on 22 March 1888 there were dark rumours of suicide, but his death certificate records 'cardiac disease'. His fall is the most spectacular instance of the way in which (in the phrase of the day) the spin of the wheel of commercial fortune brought down some of Auckland's most successful businessmen.