Thomas C.J. Bain was the second son of Andrew G. Bain* and his wife Maria E. von Backstrom. At the age of sixteen he participated as a volunteer in the Seventh Frontier War of 1846-1847, helping to guard the women and children seeking refuge in the church in Fort Beaufort. He received little formal education and from April 1848 was an assistant to his father for about five years, during the building of Michell's Pass and Bain's Kloof. The excellent practical training he received turned him into the foremost mountain road builder in southern Africa, outshining even his famous father. He was promoted to inspector of roads in the civil service of the Cape Colony in November 1853. Early in 1854 he passed an examination in civil engineering set under the direction of the Colonial Engineer, C.C. Michell* and the Superintendent-General of Education for the Cape, obtaining the best marks of the five candidates. That same year he succeeded his father as inspector of roads for the Western Cape, and in June married Johanna Hermina de Smidt, daughter of the secretary of the Central Roads Board, W.A.J. de Smidt. The third of their twelve children, Georgina J. Bain, married Joseph S. Lister*, the first chief conservator of forests at the Cape.
Thomas constructed or improved 23 major mountain roads during his career as a road builder, often working on several of them at the same time, sometimes hundreds of kilometers apart. He was extremely busy, travelled widely on inspection trips and spent much time surveying new roads on horseback. From the results of these surveys he drew up meticulous maps and working drawings as well as estimates of costs. His first project was Grey's Pass, through Piekenierskloof near Citrusdal in 1857-1858. The others included famous passes such as Prince Alfred Pass (1864-1867), Tradouw Pass (1869-1873), Pakhuis Pass (1874-1877), Meirings Poort (1879), the road from Knysna to Humansdorp through the Grootrivier, Bloukrans and Stormsrivier ravines (1879-1885), Van Rhyn's Pass (1882), and Swartberg Pass (1884-1887). This work was of paramount importance in establishing proper road communications to many isolated areas of the colony. Yet he did not occupy a very senior position in the civil service: In 1869 he was but one of eleven inspectors of roads and other public works reporting to the Chief Inspector of Public Works, M.R. Robinson*. In addition to his road building he served as district engineer in the Cape Government Railways from March 1873 to august 1874, working on the railway line through Tulbagh Kloof. In 1877 he became an associate member of the (British) Institution of Civil Engineers.The last road that he built was that from Sea Point to Hout Bay, a breathtaking route along the coast completed in 1888.
Thomas inherited from his father a serious interest in science, particularly in geology, palaeontology, archaeology and botany. He collected stone artefacts in the course of his work, cataloguing them meticulously. In 1880 he made a superficial excavation in a cave in the Knysna Heads, which yielded a child's skull associated with various artefacts, including a shoulder blade bone with paintings on it. The site was described in a note, "Bone caves at Knysna", in the Cape Monthly Magazine (Series 3, 1880, Vol. 2, pp. 255-256). In 1886 he exhibited a collection of stone tools and other archaeological artefacts, including the painted shoulder blade, at the Colonial and Indian Exhibition in London. A collection of his stone artefacts, augmented by his son John Montagu Bain*, was donated to the South African Museum in 1903. After devising a technique for tracing and colouring rock paintings he made copies of rock art at twelve different sites. A number of copies, made near Clanwilliam, were presented by him to the South African library in 1878.
The governor of the Cape, Sir Henry Barkly*, himself an enthusiastic plant collector, asked Bain to collect plants and this resulted in his discovery around 1875 of four new species of stapelias (Fam. Asclepiadaceae), described by N.E. Brown*. Another plant of the same family, Hoodia bainii was named after him by R.A. Dyer*. His knowledge of the Knysna area led to the publication of a booklet, Knysna district, in the division of George, Colony of the Cape of Good Hope (London, 1871), which he wrote in support of a scheme by O. Brierly, artist on Prince Alfred's staff during the latter's visit to Knysna, to encourage British immigration to the region. Among other information it listed 41 varieties of timber.
Bain's earliest geological publication was a booklet, An attempt to account for the origin of the Cape diamond... (Cape Town, 1870). In 1871 he accompanied W.G. Atherstone* on a trip to investigate the reported discovery of gold in the Koup region, between the Swartberg and Nieuweveld ranges, but no gold was found. Their Report on a tour in connection with reputed gold discoveries in the Gouph was submitted to parliament that same year. Bain then published three geological papers in the Cape Monthly Magazine (2nd series): "Prospecting for gold in the Bokkeveld" (1874, pp. 300-304); "Search for gold in the Knysna region" (1876, pp. 191-192); and "Notes on the geology of the western districts" (1877, Vol. 15, pp. 171-178). After E.J. Dunn* had reported favourably on the Millwood goldfields near Knysna, Bain was appointed acting mining commissioner there. He investigated the finds and, with C.F. Osborne*, reported positively in May 1886, whereupon he, G. Shepstone and P. Fletcher* snr were appointed as the Millwood Gold Commission. The Commission reported on the workings to parliament in 1887, but though some 400 miners worked about 2000 claims there at the time, most soon left for the newly discovered Witwatersrand goldfields. Bain again reported on the goldfields to parliament in 1889. His other geological reports to parliament included reports on a tour of inspection to the gold-bearing regions of the Prieska district and Griqualand West (with P.D. Hahn*, 1887 and 1888); the alleged discovery of gold near Oudtshoorn (with P.D. Hahn, 1889); the discovery of gold near Prince Albert (1891); the coal measures in the Eastern Province (1891); and the discovery of lead in Griqualand West (1893). He was also constantly concerned with the search for water, and in 1885 and 1886 published two booklets, Practical hints on water finding in connection with geology, and on the construction of dams, and Water-finding, dam-making, river utilization, irrigation.
Meanwhile, in 1888, he was "detached" from the Roads Department and appointed geological and irrigation surveyor of the colony. In this new post he first visited Van Wyk's Vlei, where Mr Garwood Alston* had surveyed lines of furrows to divert the Carnarvon River and together they proceeded to Prieska, where they found that irrigation of the town lands by the Orange River would not work. In 1889 the British palaeontologist H.G. Seeley* visited the Cape and Thomas took him to various fossil sites in the Karoo. This was done at the government's request, as fossils were thought to be associated with coal deposits. Bain had extensive experience of fossil hunting by this time, as he had collected for the British Museum. He had also received a small government grant in 1882 to collect Dicynodon fossils for the South African Museum, which led him to undertake a collecting trip in 1883. Seeley and he found a specimen at De Bad, at the foot of the Nieuweveld range, that Seeley named Bradysaurus bainii. They also compiled a joint report on mineral deposits investigated during their tour, which was published as an annexure to Bain's annual report to parliament for 1889. Seeley came to regard him as a close friend. The post of geological and irrigation surveyor, like his former post, required constant travel and led him to report on irrigation schemes, dams, mines and mineral deposits all over the colony. One of his last tasks in the field was a geological investigation in connection with underground water supplies in British Bechuanaland, from Vryburg to Palah Camp on the Crocodile River.
When the short-lived South African Geological Association (1888-1890) was founded in Grahamstown in June 1888, Bain was elected vice-president for the Cape Colony. He was also a member of the South African Philosophical Society (founded in 1877) for a few years to about 1881. He had musical talents too, his favourite insturment being the violin. When he became ill in 1893 and died on his 63rd birthday he had worked for the Cape government continuously for 45 years, during which time he appears to have taken only one month leave. He was a quiet, modest and gentle person, who none the less could successfully supervise several large work forces simultaneously in different places; a man of many talents, with a keen sense of humour.