The eldest child of Eliza Ball and her husband, Matthew Philson, a mathematics master at a large private school, Thomas Moore Philson was born at Londonderry, County Londonderry, Ireland, probably on 10 August 1817. He was educated by his father before entering the University of Edinburgh in 1834. After graduating MD and MRCS in 1839, and taking the Ballingall prize in the class of military surgery, Philson served as an assistant in a medical partnership in the Forest of Dean, Gloucestershire, for three years. He married Matilda Willmet Anderson at Chatham, Kent, on 24 December 1844; they were to have six daughters and three sons.
In October 1843 Philson received a commission as assistant surgeon to the 58th (Rutlandshire) Regiment of Foot, and in June 1845 he and his wife accompanied it to Sydney, Australia. The regiment was soon ordered to New Zealand under Colonel R. H. Wynyard, and was sent almost immediately to the Bay of Islands. Philson saw military action there, including the battle of Ruapekapeka in January 1846, for which he was mentioned in dispatches. The regiment remained in the Bay of Islands until it was moved to Wellington and, later, to Wanganui.
Resigning his commission, Philson entered private practice in Auckland in 1851. His military connections were continued, however; he was appointed surgeon to the Auckland Regiment of Militia in December 1856 and again in April 1860, and in April 1887 he was appointed brigade surgeon to the New Zealand defence forces, with the rank of lieutenant colonel.
Philson was still a comparatively young man when he commenced his private practice, but he soon became well known for his medical and administrative skill. Within 10 years he held all the important medical administrative posts in Auckland, being appointed coroner in 1858, provincial surgeon and superintendent of Auckland Hospital in 1859, and port health officer in 1860. He also served as medical officer to the prison at Fort Cautley, to the Mount Eden gaol and to the Provincial Lunatic Asylum.
As Philson's ability in medicine and surgery became widely known throughout New Zealand, many patients came from other parts of the country to gain the benefit of his expertise. His medical skills were complemented by an altruistic devotion to duty. When the mail steamer Nebraska arrived from Sydney in 1872, one of the crew was found to be suffering from smallpox. It was the first occurrence of the disease in Auckland, and every precaution was taken to contain the infection. Philson, a victim of smallpox in his youth, isolated himself with the patient until he died. He then attended to the funeral arrangements alone and maintained his isolation, even from his family, for several weeks to ensure safety from infection. The superintendent of the province conveyed the very warm appreciation of the provincial government for this singular devotion to duty, presenting Philson with a cheque for £100.
Hospital records of the decade from 1865 contain several detailed reports by Philson revealing the generally makeshift conditions in the hospital at that time; they emphasise the lack of accommodation, the inadequate water supply and the need for better facilities. Philson made recommendations and outspoken comments as he saw the need, while there were at times frank references to the hospital in the local newspaper. His complaints proved effective, and the provincial government decided in 1875 that a new hospital should be constructed.
Auckland's second hospital was opened in 1877 with Philson as medical superintendent. He retired in 1883, largely because of a serious disablement of his right hand through septic poisoning acquired during surgical practice. He was then appointed the first member of the honorary consulting staff. Philson's retirement was marked by a public acknowledgement of his outstanding service to the community; an illuminated address was presented to him along with a gold watch and chain and a purse containing 270 sovereigns. With characteristic generosity Philson handed the money over for the establishment of a trust fund to found a medical library for the use of students. From this fund books were occasionally bought and added to the Auckland University College library, but it was almost 90 years before the Philson Library became a reality in the university's medical school.
Thomas Moore Philson was noted for unbending integrity, a sympathetic understanding of his patients, and a remarkable devotion to their needs. He was a co-founder and member of the Auckland Baptist community and attended the Auckland Baptist Tabernacle for many years, as well as supporting other benevolent societies. He led his family in daily prayers, and accompanied their singing of psalms on the flute or harmonium. His death at Auckland on 22 November 1899 removed a pioneer who had laboured to develop the infant town's medical services. Matilda Philson died at Auckland on 5 September 1908.