John Patrick Fitzgerald was born in Carrickmacross, County Monaghan, Ireland, probably in 1815, to Patrick Henry Fitzgerald and his wife, Anne Dunoyer. He graduated MD from the University of Glasgow in 1839, completed the requirements for membership of the Royal College of Surgeons in London, and was awarded a Diploma in Obstetric Medicine from the Britain Street Lying-in Hospital, Dublin.
Fitzgerald embarked as surgeon superintendent on board the New Zealand Company's vessel Oriental on 15 September 1839, landing at Port Nicholson (Wellington) on 31 January 1840, to begin work as consulting physician to the infirmary of the Wakefield settlement. Soon after, Lieutenant Governor William Hobson appointed him coroner and health officer in Port Nicholson. On 14 November 1842 he married Eliza Sarah Christian, the daughter of a Dublin solicitor, in Wellington.
In 1845 Fitzgerald was appointed surgeon to the Wellington Militia, and on 15 September 1847 became the superintendent of Wellington's public hospital, a two-storeyed building accommodating 16 patients. He was obliged to provide assistance to 'the jail, the police, the natives, pauper Europeans, and in fact all to whom the government may be desirous of affording medical attendance'.
A medical practitioner with advanced techniques, he advocated community sanitation, improved ventilation of homes and hospitals, the use of vapour baths, the wrapping of fever patients in layers of wet blankets, and the use of anaesthesia. Wellington Hospital was open to Maori, much of whose illness he attributed to filthy blankets, bad sleeping accommodation, unbalanced diet and dwellings without chimneys.
Fitzgerald's Catholicism and his cures attracted critics; the strongest were two politicians qualified in medicine: Isaac Earl Featherston, who had been surgeon superintendent aboard the Olympus and who became superintendent of Wellington province, and William Fitzherbert, who had studied medicine in Paris and London. Both detested Fitzgerald and supported John Dorset, surgeon to the infirmary. Dorset used Featherston's newspaper, the Wellington Independent, as a vehicle for his attacks, and Fitzherbert saw to Dorset's appointment to committees authorised to investigate Fitzgerald's qualifications and medical practices.
Fitzgerald led the Catholic community at Wellington until Father Jeremiah O'Reily arrived in 1843. He remained the leading Catholic layman. On 21 November 1850 Richard Taylor, a Church Missionary Society cleric, complained that Fitzgerald gave extra visiting privileges to Catholic priests and assisted their proselytising. Governor George Grey ordered an investigation and on 10 December 1850 a board of visitors judged the general charge proved.
On 26 March 1851 Dorset charged Fitzgerald with 'gross quackery' and with fraudulent use of medical qualifications. A provincial council select committee, chaired by Dorset, investigated the second charge and on 29 January 1854 expressed itself entirely satisfied that his qualifications were authentic.
By 1854 Fitzgerald had practised in Wellington for 15 years without leave. His wife had died on 4 April 1852, three weeks after the birth of their fifth child; a daughter was afflicted with a heart ailment; and in 1853 Fitzgerald himself had survived cholera. He requested two years' leave, but this and two subsequent requests for shorter leave periods were refused with derision. On 31 July 1854 Fitzgerald resigned as hospital superintendent and soon after departed for Britain. The provincial council judged him in dereliction of duty and for several years he was obsessed with the preparation of a petition to Queen Victoria praying for a redress of wrongs.
In 1856 Fitzgerald went to King William's Town, Cape Colony, and was appointed superintendent of Grey Hospital, built by George Grey, then governor of Cape Colony. Thirty-two years later he returned to Britain and died at Ramsgate, England, on 8 January 1897.