He first co-founded Newcastle's Eye Infirmary, with John Fife, and then the Medical School. He worked at the Newcastle Infirmary, later renamed the Royal Victoria Infirmary, for many years and was instrumental in its expansion in the 1850s.
Edward Headlam Greenhow, his brother's son, was also a physician-educationalist, who made his mark in epidemiology and public health.
Thomas married Elizabeth Martineau, daughter of Thomas Martineau and Elizabeth Rankin, of the prosperous, socially reformist Martineau family, mainly based in Birmingham. His wife's siblings included the religious philosopher James and the sociologist and political theorist Harriet.
^ ab"Newcastle Infirmary Time Line 1801–1849". Newcastle University. Retrieved 19 July 2013. 1832: Thomas Greenhow appointed honorary surgeon to the Infirmary. He had already been surgeon to the lying-in hospital, and in 1822 had established the Eye Infirmary with John Fife.
^Bettany, G. T. (2004). "Fife, Sir John (1795–1871), surgeon and politician". Oxford Dictionary of National Biography. Oxford University Press. Retrieved 19 July 2013. He [Fife] specialized in diseases of the eye, founding in 1822, with T. M. Greenhow, a charity which became the Newcastle Eye Infirmary.
^"Newcastle Infirmary Time Line 1850–1888". Newcastle University. Retrieved 19 July 2013. 1850: Mr Greenhow, as spokesman for the honorary medical staff, points out that again the Infirmary is inadequate for the needs of the area, which had tripled in population in the last 100 years. The annual report draws the attention of the governors and public to the Infirmaries shortcomings. 1851: Greenhow and Gibb visit hospitals in London and elsewhere to gain insight in modern hospital design, and report back to the committee. On March 13th John Dobson, the famous architect, laid his plans for a new wing and redevelopment of the Infirmary before the committee, and they were agreed on April 3rd. 1855: The Dobson Wing opened, costing £10 500.
^Entry in Plarr's Lives of the Fellows Online, a biographical register of the Fellows of the Royal College of Surgeons of England, written by its librarian Victor Plarr (1863-1929), and hosted by the College