Uniacke, John James FitzGerald (1797–1825), explorer, writer, and early official in New South Wales, was born 4 July 1797 on Charlotte's Quay, Cork, second son and sixth of nine children of Robert Uniacke (1756–1802) of Woodhouse, Stradbally, Co. Waterford, MP for Youghal 1777–1800, and Annette Constantia Uniacke (b. 1760), daughter of John Beresford (qv) (1738–1805). John Uniacke was educated privately before being admitted to TCD (3 October 1814). He was then sent to St John's College, Cambridge, in Michaelmas term 1816 as a pensioner. College records show that he failed to graduate in 1819 because of a two-term absence (1817–18). Little is known of his whereabouts until May 1823, when he embarked as acting chaplain to 160 male convicts in the 425-ton Competitor, reaching Hobart Town on 3 August 1823. His letters to his mother (NAI, Uniacke papers) describe the voyage and his experiences in New South Wales. After landing at Sydney Cove (late August), he volunteered as supercargo for an expedition led by John Oxley, the surveyor-general, which left in the Mermaid (23 October 1823). Uniacke recorded the main events in his ‘Narrative of Mr Oxley's expedition to survey Port Curtis and Moreton Bay . . .’, published in Barron Field (ed.), Geographical memoirs on New South Wales (London, 1825). On the return journey Uniacke wrote down the tales of the convicts Pamphlet and Finnegan, the first white men to explore the Brisbane River, in ‘Narrative of Thomas Pamphlet . . .’ (Field, op. cit., pp. 87–129).
Uniacke was appointed (20 February 1824) superintendent of distilleries with a salary of £200 a year, and was granted 2,000 acres at the request of Earl Bathurst, secretary of state for the colonies. On 24 June 1824 he was temporarily promoted to sheriff and provost marshal for the colony of New South Wales and its dependencies, excluding Van Diemen's Land, but on the arrival in July of John Mackaness (1770?–1838) reverted to his former position. On 13 January 1825 he died suddenly of a remittent fever at the age of 27; he was unmarried and had no issue. The Sydney Gazette and New South Wales Advertiser published an obituary (20 January 1825); the funeral was attended by the colonial secretary, all the colony's dignitaries, and every officer in the garrison. His remains were interred in the Devonshire St. cemetery, on a site later occupied by Sydney central railway station. In 1901 his monument was transferred to a new cemetery bounded by Bunnerong Road, La Perouse. His personal effects and property, including a gig, three horses, a four-poster bed, and 2,000 acres, were sold at public auction soon after his death. A commemorative edition of his writings on the Moreton Bay expedition was published (1998) by the Royal Historical Society of Queensland.
His elder brother Robert John (1795–1851) inherited Woodhouse (1802), had a distinguished army career (serving under Wellington (qv) in the Peninsular and Waterloo campaigns), and married (2 August 1821) Mildred Bourke; they had children. Of his seven sisters, Nannette Helen (b. 1796) was an accomplished artist. A painting of the yacht of the marquis of Waterford, ‘The Gem in a storm’ (1841), is attributed to her.