John Nunn Eagle, medical practitioner, was the son of Francis Eagle and his wife Sarah Ann, born Sprague. He studied medicine in England and has been credited with having obtained the degree Doctor of Medicine (Laidler & Gelfand, 1971, p. 309), although no qualifications are listed against his name in the South African Medical Directory for 1897. With his family he emigrated to Natal, where he arrived in November 1849. He soon moved on to Colesberg where he worked as locum tenens and acting district surgeon, but his medical qualifications were not recognised by the medical authorities in the Cape Colony. In 1854 he therefore moved to the Orange Free State and settled in Fauresmith as medical officer. In 1862 he moved to Philippolis, and from February 1864 practiced at Otterspoort near the town for the rest of his life, with two interruptions: one to serve as medical officer to the Free State forces during the Basuto War of 1865-1866, and another to work on the diamond fields at Pniel in 1870 (he was declared insolvent that same year). In March 1863 he was registered as the first qualified medical practitioner in the Orange Free State (there were a number of unqualified earlier practitioners on the register). In the late 1890s he was a member of the (second) South African Medical Association. During the period 1859 to 1881 he requested and received vaccine lymph several times, presumably for use in his medical practice.
In 1891 Eagle began meteorological observations at Philippolis for the Cape of Good Hope Meteorological Commission. Six years later his station was upgraded to a second order meteorological station, one of only two in the Orange Free State. He continued his observations to 1899. After his death the next year, as a result of cancer of the kidneys, the station was closed.
Eagle had wide interests and led an eventful life. He was a devoted gardener; had two farms, Otterspoort and Vogelfontein, where he refined the wool of his merino sheep; did legal work such as drafting wills; had an extensive knowledge of the world's literary classics; imported a printing press and performed some printing work for the government; and was a friend of president Brand. In 1880 he translated a portion of a work by J. Voet, Commentarius ad Pandectas (Book 47, title 10, on injury and libel) into English and published it in Philippolis. Around the same time he acted as editor of Reports of cases decided in the High Court of the Orange Free State... [in 1874-1878], compiled by A.P. de Villiers, and published it in three parts in Philippolis in 1879-1880. He was married in England in 1844 to Emily Ashford, who died in 1885. They had a son and six daughters.