Richard Nathaniel Rubidge was the son of Captain Robert Henry Rubidge of the Royal Navy, and his wife Hannah P. Jones. His parents emigrated to the Cape Colony in 1821 and Richard grew up on a farm in the Grahamstown district. He and William G. Atherstone* were apprenticed to the latter's father, Dr John Atherstone*, in Grahamstown. Rubidge later completed his medical education at the University of London in 1843, qualifying as a Bachelor of Medicine (MB) and member of the Royal College of Surgeons (MRCS). Upon his return to the Cape he was licensed to practice in April 1844 and did so in Graaff-Reinet and from 1850 in Port Elizabeth. He served as surgeon to the new Provincial Hospital in Port Elizabeth, which was initiated in 1856, and remained associated with it for the rest of his life. During 1858-1859 he and Dr George Dunsterville had to treat over 200 cases of smallpox in a temporary building, until the hospital was completed in August 1859.
Rubidge was interested in natural history and, as a result of his friendship with W.G. Atherstone and Andrew Geddes Bain*, more particularly in geology and palaeontology. In 1854 he was sent by a group of Grahamstown merchants to investigate the discovery of gold at Smithfield in the Free State. As a result of this investigation he submitted his first paper, "On the occurrence of gold in the trap-dykes intersecting the Dicynodon Strata of South Africa" to the Geological Society of London. It was published in the Quarterly Journal of the Geological Society (1855) and was soon followed by his "Notes on the geology of some parts of South Africa" (1856) and, after accompanying W.G. Atherstone to Namaqualand during 1854-1855, "On the copper mines of Namaqualand" (1857).
One of his specific geological interests was the formation of metamorphic rocks and he was inclined to see the effects of metamorphism in several situations where other explanations have since prevailed. Some of his observations relating to this topic were published in two papers: "Notes on the metamorphosis of rocks in South Africa" (1862) and "On the metamorphosis of rocks in the Cape Town district, South Africa" (1862), both in The Geologist. With regard to the stratigraphy of South Africa he contributed several papers to British journals: "On some points in the geology of South Africa" (Quarterly Journal of the Geological Society, 1958), in which he introduced the names Table Mountain Sandstone and Ecca Series; "On the relations of the Silurian schists with the quartzose rocks of South Africa" (Geological Magazine, 1864) and "On the changes rendered necessary in the geological map of South Africa by recent discoveries of fossils" (Quarterly Journal of the Geological Society, 1865. Other papers appeared in local journals, particularly in the short-lived Eastern Province Magazine (1861-1862): "The clay-slate and its fossils" (Vol. 1, pp. 148-155, 195-200, 234-237), "Recent rocks" (Vol. 2, pp. 29-32), "The dicynodont formation" (Vol. 2, pp. 111-115, 173-177), and "Physical features of the Eastern Province" (Vol. 2, pp. 229-233). This journal should not be confused with the earlier Eastern Province Monthly Magazine (1856-1858) in which Rubidge also published two papers. Some of his conclusions relating to the correlation of strata differed from those of A.G. Bain* and E.J. Dunn* and were later proved wrong, for example, he mistakenly correlated the Malmesbury slates with the Bokkeveld Group, and the Table Mountain sandstone with that of the Witteberg Group. These conclusions were accepted by some other investigators during the next two decades and stimulated further investigations.
Rubidge collected many fossils from the rocks of the Uitenhage Group and the Karoo Supergroup. He is credited with making the earliest reported collection of fossil plants of any age in South Africa, at Dunbrody along the Sundays River in 1845, and also was the first person to collect plant fossils in the Molteno Formation, at Jakkalskop in the Free State, about 1850. Some of his early fossil finds, from the Uitenhage Group along the Sundays River, were described by J.E. Portlock before the British Association in 1851. At the same meeting W.H. Harvey* briefly described the plant fossils Rubidge had collected at the same site. Rubidge recognised that the fossil plants of the Karoo were related to the Glossopteris fauna of India and Australia. He donated many fossils to the South African Museum, Cape Town, in 1857. A collection that he sent to the Geological Society of London in 1859 was described by R. Tate ("On some secondary fossils from South Africa", Quarterly Journal of the Geological Society, 1867), who named the fossil plant genus Rubidgea and the species Dictyopteris rubidgea in his honour and also discussed his earliest finds at Dunbrody. In 1876 some of his vertebrate Karoo fossil remains were described, with others, by Professor Richard Owen*. Dr Robert Broom* named the species Dicynodon rubidgei after him in 1932. He was elected a Fellow of both the Geological Society of London (FGS) and of the Linnean Society (FLS).
Rubidge also collected living plants around Graaff Reinet and Port Elizabeth, and in the south-western Cape. These are now in the Bolus Herbarium, University of Cape Town. His ferns were sent to Dr C.W. Ludwig Pappe* and several are cited in Pappe and Rawson's Synopsis filicum Africae Australis (1858). Rubidge played an active role in the activities of the Port Elizabeth Natural History Society which flourished briefly during 1866-1867. He also served on the committees of the Port Elizabeth Athenaeum and the Port Elizabeth Public Library.
Rubidge never married. He died suddenly at the age of 46 from a self-administered dose of strychnine that he had taken in the belief that it would be beneficial for what he believed to be a weak heart. After his death W.G. Atherstone wrote to his son "[His] death is a tragic blow to our little scientific circle, too few of us at present and too scattered to do much good."