Charles K. Brain, son of Robert Brain and his wife Mary E. Kimberlin, studied entomology for some time at the University of Manchester, but circumstances made him take up school teaching as a career. He came to the Cape Colony in July 1903 and was on the staff of the South African College School in Cape Town for several years. Meanwhile he collected and studied insects and other invertebrates in his spare time, particularly from an economic perspective. For example, in 1907 he presented several interesting specimens of marine invertebrates and some rare insects to the South African Museum. In June 1909 he succeeded R.W. Jack* as assistant in the Cape Town office of the government entomologist, C.P. Lounsbury*, with responsibility for the inspection of plants and fruit entering the colony from overseas. During the next two years he prepared himself for further studies in entomology. In 1911, shortly after the formation of the Union of South Africa, he was awarded a government scholarship of 200 pounds sterling per annum and leave of absence for three years to study entomology at Ohio State University in the United States, where he was awarded the degree Master of Arts (MA). For a short period he served as entomologist to the Ohio State Board of Health. During 1912-1913 he published four papers on insect pests in the Annals of the Entomological Society of America. The next year he was awarded the degree Doctor of Science (DSc) by the University of Birmingham with a thesis entitled Contribution to the study of mealy bugs of the tribe Pseudococcini (Coccidae), with special reference to the genus Pseudococcus (1914).
Brain returned to South Africa in July 1914 and was appointed as entomologist in the Division of Entomology of the Union Department of Agriculture, Pretoria, where he was involved mainly in laboratory work for the next few years. At this time he began to concentrate on the study of scale insects (superfamily Coccoidea), of which he made an important collection. His work on the group was published in, among others, five substantial papers under the title "The Coccidae of South Africa". The first of these appeared in the Transactions of the Royal Society of South Africa (1915, Vol. 5, pp. 65-194) and the other four in the Bulletin of Entomological Research (1918-1920, Vols 9-11, 150p). As co-author with Claude Fuller* he also contributed a short paper on "Curious African Coccids" to the Bulletin of the South African Biological Society (1918, No. 2, pp. 1-4).
In 1920 Brain resigned his post in the Division of Entomology and on 1 October that year succeeded E.S. Cogan* as professor of entomology at Stellenbosch University. There he described "The intracellular symbionts of some South African Coccidae" (Annals of Stellenbosch University, 1923, Section A, Vol. 1(2), 48p), which included descriptions of seven new genera and eleven new species. This was followed by a "Host plant index of South African scale insects (Coccidae) with a list of species found on each plant recorded" (Ibid, 1924, Section A, Vol. 2(2), 44p) - an alphabetical list of host plants and the scale insects found on each of them. He also published a brief but interesting "Preliminary report on the adaptation of certain radio principles to insect investigative work" (Ibid, 1924, Section A, Vol. 2(2), 4p) in which he described the detection and amplification of the sound of gnawing of quince borer larvae inside the stems of apple trees and the detection of weevils in grain, as well as the agricultural application of these techniques.
In 1926 the Elsenburg Agricultural School was amalgamated with the Faculty of Agriculture of Stellenbosh University to form the Stellenbosh-Elsenburg College of Agriculture. Brain was appointed as the first principal of the college (while retaining his appointment as professor of entomology), serving in this capacity until he resigned on 1 June 1929. During his time at the college he wrote Insect pests and their control in South Africa (Cape Town, 1929, 468p) - the first (and for years the only) comprehensive text dealing with local insect pests after Miss E.A. Ormerod's* small volume in 1889.
Upon resigning from the college Brain became director of agriculture of Southern Rhodesia (now Zimbabwe) and was stationed in Salisbury (now Harare). Within the first year he reorganised the department, combining several of its branches into a Division of Animal Industry (headed by J.M. Sinclair*) and a Division of Plant Industry (headed by H.G. Mundy*). He also extended his interests to include botany and published "A key to the sedges (Cyperaceae) of Southern Rhodesia" (Proceedings of the Rhodesia Scientific Association, 1934, Vol. 33, pp. 51-96) and several articles in the Rhodesia Agricultural Journal.
Brain was an active member of several scientific societies. By 1906 he was already a Fellow of the Entomological Society (England) and that year joined the South African Philosophical Society as a member. He remained a member when it became the Royal Society of South Africa in 1908, and was elected a Fellow of the latter in 1924. During 1916 and 1917 he was the first honorary secretary and served on the central executive committee of the South African Biological Society, created by the amalgamation of the Transvaal Biological Society and the South African Ornithologists' Union. However, the fact that he was often away from Pretoria during 1917 resulted in a gap in the society's minutes. In Zimbabwe he joined the Rhodesia Scientific Association in 1929. In January 1920 he married Zoe Findlay, who had trained as a botanist, and with whom he had two sons and two daughters. One of his sons, C.K. (Bob) Brain later became director of the Transvaal Museum.