Nicholas E. Brown showed an interest in plants while still at school, before the age of 18. After completing his school education he became curator of a private museum established by the naturalist W.W. Saunders at Reigate, Surrey. His interest in botany was further stimulated by Saunders and his collaborators, who produced a five volume work, Refugium botanicum ... during 1869-1873. The Stapeliads (family Asclepiadaceae) were his first love and remained a life-long hobby. In February 1873 he was appointed as an assistant in the herbarium of the Royal Botanical Gardens at Kew, near London. The next year he started lecturing to the young gardeners at Kew on geographical botany. For some time his botanical work was restricted to the flora of England, but from 1886 he became intensely interested in the flora of tropical Africa and South Africa.
Brown had a weak constitution and hence was not a plant collector, and never visited South Africa. In 1909 he was promoted to assistant keeper, remaining at Kew until his retirement in 1914. After retiring he continued working in the Kew herbarium. He was married to the daughter of plant collector Thomas Cooper*.
Brown's numerous botanical publications appeared from 1876 to 1937, the latter a few years after his death. Early on he developed a general interest in succulents, stimulated by the collections sent to Kew from the Cape Colony by Sir Henry Barkly* during 1873-1877. He described these plants in a paper entitled "Stapeliae barklyana", which appeared in the third series of J.D. Hooker's* Icones plantarum (1890). Later he became interested in every branch of botany, from microscopical dissection to the taxonomy of entire families. He made important contributions towards the taxonomy of South African plants, particularly in the families Asclepiadaceae, Mesembryanthemaceae, and Labiatae. For example, from 1901 to 1925 he contributed descriptions of 14 families, or parts of families, to the Flora Capensis, then edited by W.T. Thiselton-Dyer*, including the Asclepiadaceae (1909, Vol. 4(1), pp. 518-1036), the smaller genera of Ericaceae, the genus Euphorbia, and several families of aquatic plants. His monograph on the flora of Ngamiland was published in Kew Bulletin (No. 3) in 1909. After his retirement he became an expert not only on South African plants, but also on its geography. He was a painstaking worker, and probably did more work than any other person on South African succulents. In 1921 he began the more detailed sub-dividing of the genus Mesembryanthemum into some 75 genera, describing most of them in the Gardener's Chronicle. In 1931, in collaboration with A. Tischer and M.C. Karsten, he published the work Mesembryanthema. It appears that he looked upon this genus as his private territory, for he seems to have resented the German botanist Prof. G. Schwantes for his work on it, leading to some quarrels between them in German gardening journals.
Brown contributed substantially to A manual of the flowering plants and ferns of the Transvaal... by J. Burtt Davy* (1926). Articles by him published in South African journals include two descriptions of new species in the Annals of the Transvaal Museum (Vol. 2(1), 1909; Vol. 2(3), 1910); "The genera Aloe and Mesembryanthemum of Thunberg's herbarium", in Bothalia, (1923, Vol. 1(3), pp. 139-169); "Contributions to a knowledge of the Transvaal Iridaceae" in the Transactions of the Royal Society of South Africa (1929, Vol. 17, pp. 341-352; 1932, Vol. 20, pp. 261-280); "Nivenia Vent. and Nivenia R.Br." in the same journal (1933, Vol. 21, pp. 259-270); "Freesia Klatt, and its history", on a South African genus of the Iris family, in the Journal of South African Botany (1935, Vol.1, pp. 1-31); and "Helixyra simulans" in Flowering Plants of South Africa in 1936.
Brown has been described as "a quaint-looking, rather hunched little man with a narrow face and a small goatee beard ... ever ready to share his vast knowledge of South African plants". He was elected an associate of the Linnean Society in 1879. In 1921 he was awarded the Captain Scott Memorial Medal of the South African Biological Society, and in 1932 the honorary degree Doctor of Science (DSc) was conferred on him by the University of the Witwatersrand. The genus Brownanthus and some species of plants were named in his honour.