Gerald E.H. Barrett-Hamilton, a British zoologist and marine biologist, was educated at Trinity College, Cambridge, where he obtained a first class pass in the natural science tripos in 1894. By that time he had already published three botanical papers: "Plants found near new Ross, Ireland" (with L.S. Glascott; Journal of Botany, 1889), "Plants found near Kilmanock, Co. Wexford" (also with Glascott; ibid, 1890), and "The characteristic plants of Co. Wexford" (with C.B. Moffat; Irish Naturalist, 1892). He was called to the Bar in 1896, but during 1896-1897 served as a member of the Bering Sea Fur-Seal Commission. Subsequently he published his Report by Mr. G.E.H. Barrett-Hamilton on his mission to the Russian seal islands in 1897 (London, 1899, 67p) as well as two papers, "On two subspecies of the arctic fox (Canus lagopus)" (with J.L. Bonhote; Annals and Magazine of Natural History, 1898) and "A visit to Karaginski Island, Kamchatka" (with H.C. Jones; Geographical Journal, 1898). In 1900 he was a candidate to accompany Captain Robert F. Scott's first expedition to Antarctica as its naturalist, but the choice fell on his friend Dr. Edward Wilson. Barrett-Hamilton described the seals collected by the Belgian antarctic expedition of 1897-1899 in 1901, and those of Scott's expedition in Reports on the collections of... the "Southern Cross" in 1902.
In 1901 he came to South Africa and served in the Anglo-Boer War (1899-1902) as a captain in the Royal Irish Rifles. He spent most of his time in the north-eastern Free State, western Transvaal, and Griqualand West, and in 1902 donated some 90 mammal and bird skins from these areas to the South African Museum. This donation was followed up with a further 15 bird skins in 1903. In the same year he published a paper on "Traces of past glacial action in the Orange River Colony, South Africa" in Nature (Vol. 67, p. 223). He also collected plants during his stay in South Africa and three plant species were later named in his honour.
Barrett-Hamilton later worked in the British Museum (Natural History). He described many new species of small mammals from the islands around the British Isles and many other mammals from around the world. He became a member of the British Association for the Advancement of Science in 1899. He was promoted to major in 1905, at which time he resided in Arthurstown (near Waterford) in the south of Ireland. From 1910 he was the editor of A history of British mammals, which was illustrated by Dr. Wilson. Its completion was prevented by the premature deaths of both men. Barrett-Hamilton was married to Maud Charlotte Eland, of Ravenshill, Transvaal, with whom he had six children. He died while leading a British government investigation into the whale and seal fisheries on the island South Georgia.