John Hewitt, zoologist and museum director, was the eldest child of John Hewitt and his wife, Rebecca Smith. He showed an intense interest in science from an early age. With the help of scholarships he entered Jesus College, University of Cambridge, in 1899. Four years later he obtained a first-class pass in the natural science tripos and was awarded the degree Bachelor of Arts (BA). During 1903 he served as biologist on a bathymetric survey of Scottish lochs and later published a paper on the plankton found on various islands off the north and west coasts of Scotland in Scientific Research of the Bathymetric Survey of Scottish Freshwater Lakes (1910). After graduating he taught for two years, first at Blackheath Mission School and then as science master at Stoneyhurst Jesuit Training College. In 1905 he was appointed curator of the Kuching Museum, Sarawak (that part of Malaysia on the island Borneo). During the next four years he made extensive collections of insects and plants on Borneo and published ten scientific papers on various topics in the natural history and ethnography of Sarawak. In 1907 he married Florence E. Palmer, with whom he had a son and two daughters.
In 1909 Hewitt accepted an appointment as assistant for lower vertebrates in the Transvaal Museum, Pretoria. There he immediately began research in several branches of zoology, particularly on the systematics of South African reptiles, amphibians and arachnids (particularly spiders, solifuges and scorpions). During 1909 he identified reptiles for the museums in Grahamstown, King William's Town, and Kimberley. Such was his energy that ten publications by him appeared in the Annals of the Transvaal Museum during 1909-1911.
In 1910 Hewitt succeeded Dr Selmar Schonland* as director of the Albany Museum, Grahamstown - a post that he held until his retirement in 1958. In spite of a severe shortage of funds he worked with great enthusiasm and dedication to expand and improve the exhibition and study collections. Extensions to the museum were completed in 1920 and 1938, but much damage resulted from a fire in September 1941. He continued his zoological research, describing many new species. Most of his work was published in the Records of the Albany Museum, Annals of the Transvaal Museum, Annals of the Natal Museum, Transactions of the Royal Society of South Africa and South African Journal of Science. Among others he published "A survey of the scorpion fauna of South Africa" (Transactions of the Royal Society of South Africa, 1918), and a revision of the solifuges (Annals of the Transvaal Museum, 1919). Other work included his comprehensive Guide to the vertebrate fauna of the Eastern Cape Province (in two parts, 1931, 1937), written for popular use, and several important papers on the distribution of the South African fauna. His scientific work was aided by his expertise in photography.
Hewitt's research extended also into the Stone Age archaeology of the region around Grahamstown, on which he published some 20 papers. In several of these he described stone artefacts that he collected from shell middens and inland sites. He also carried out some of the first systematic archaeological excavations in South Africa. With C.W. Wilmot he excavated a cave on the farm Wilton, near Alicedale, which became the type site for the Wilton Industry. The microlithic artefacts found there, and at his excavations of sites at Glen Graig, Bergplaats, and Spitzkop, were described in his paper "On several implements and ornaments from Strandloper sites in the Eastern Province" (South African Journal of Science, 1922, Vol. 18). A few years later he and Reverend P. Stapleton provided the first description of a stone culture on the farm Howieson's Poort, which included forms typical of both the Middle and Late Stone Age. Their paper "Stone implements from a rock shelter at Howieson's Poort near Grahamstown" appeared in the South African Journal of Science in two parts (1927, Vol. 24 and 1928, Vol. 25). Subsequently he and Reverend Stapleton excavated five caves in the Cala district (1930) and a site at Tafelberg Hall, near Middelburg (1931), in order to investigate the relationship between the Wilton Industry of the Cape Fold Mountains and the Smithfield Industries of the interior. He also investigated Melkhoutboom Cave, in the Zuurberg, which he described as the best preserved Wilton site in the Eastern Cape. The material recovered there included food waste, bedding, matting, pieces of leather garments, and wooden artefacts (South African Journal of Science, 1931, Vol. 28).
Hewitt was a Fellow of the Royal Entomological Society of London (FES), a Fellow of the Zoological Society of London (FZS), and a member of the British Ornithologists' Union. He was elected a Fellow of the Royal Society of South Africa in 1913. As a member of the South African Association for the Advancement of Science he served on its council from 1912, as president of Section D in 1923, and in 1948 received honorary life membership. In 1936 he receiced the association's South Africa Medal (gold) in recognition of his outstanding research career. Upon his arrival in Pretoria he joined the Transvaal Biological Society and read three papers at its meetings during 1910-1911. In 1916 he became a foundation member of its successor, the Biological Society of South Africa, served on its editorial committee, and was elected joint vice-president for the first year. In 1943 he received the society's Senior Captain Scott Memorial Medal. As a foundation member of the South African Ornithological Society he served as joint vice-president from 1933 to 1949. He was a foundation member of the Southern African Museums Association and a member of its council for some years. In 1937 he became a foundation member of the Entomological Society of South Africa.
Hewitt received wide recognition for his research and his 160 or so publications, yet was a kind and humble man who was always prepared to help and encourage young scientists, though he expected them to perform to his own high standards. In 1935 he was awarded an honorary Doctor of Science (DSc) degree by the University of South Africa, via Rhodes University College. He continued his scientific work after his retirement, but died three years later. His papers and collections are housed in the Albany Museum, where a new wing was named after him in 1959.