Joseph Millerd Orpen was one of the nine children of Reverend Dr Charles Edward Herbert Orpen (MD), member of a family of Irish landed gentry, and his wife Alicia Francis Coane (born Sirr). Two of his older brothers were Charles S. Orpen* and Francis H.S. Orpen*. Joseph and two of his other brothers followed Charles and Francis to South Africa in December 1846, with the rest of the family following two years later. Charles senior financed his sons' farming venture on the farm Taai Bosch Fontein near De Aar. Joseph and Francis qualified as land surveyors in 1849. Two years later Joseph took part in the Eighth Frontier War against the Xhosa. In July 1852 he and Francis were appointed as surveyors in the Orange River Sovereignty (now the Free State), under the superintending land surveyor of the territory, J.H. Ford*. They worked in the Harrismith district.
Joseph Orpen was a keen fossil collector and in 1853 discovered fossil bones near Harrismith that were described by the British palaeontologist Richard Owen* the next year and named Massospondylus carinatus - the first dynosaur from outside Europe to be formally described. (A.G. Bain* and W.G. Atherstone* had found fossil dynosaur bones in rocks of the Uitenhage Group as early as 1845, but these had not been formally described). Joseph showed some of his fossils to Alfred Brown* and thus initiated the latter's interest in palaeontology (Kitching, 1991).
When Britain gave up the Orange River Sovereignty in 1854 - a move which both Orpen brothers strenuously opposed - Joseph remained in the territory and was elected a member of the Volksraad of the new Orange Free State Republic, representing Harrismith. As a result of his keen intelligence, self-confidence and interest in native affairs he was able, despite his young age, to play a part in drafting the republic's constitution and was sent on diplomatic missions to Chief Mosheshwe of the Basuto. The success of these missions led to his appointment as landdrost of Winburg, with responsibility also for Harrismith from September 1854. In addition to various official duties he surveyed the new town Kroonstad. In October 1856 he resigned his post and became a private surveyor. The next year, as a special correspondent for the Cape Argus, he wrote a treatise, History of the Basutos of South Africa, which was reprinted and published as a book (Cape Town, 1857). As a result of his outspoken support for the rights of the Basuto he was deported from the republic in 1858. On 31 March 1859 he married Elise P. Rolland (1839-1915) with whom he had at least six children.
Joseph farmed for some time near Aliwal North and carried out surveys in the Herschel and Barkley East districts for the Cape government. From 1862 he was furthermore an official mediator between Mosheshwe and the British government, playing an important role in the negotiations preceding the annexation of Basutoland (now Lesotho) by the British. In 1873 he was appointed British resident and magistrate of the region that later became Griqualand East, but resigned two years later. During that time he contributed an article to the Cape Monthly Magazine (1874, 2nd series, Vol. 9, pp. 1-13) on "A glimpse into the mythology of the Maluti Bushmen". In this article he described San mythology as told to him by a Bushman encountered in his official work. The stories were meant to explain events depicted in rock art which Joseph had copied at the request of G.W. Stow*.
While he was surveying the Hay district in Griqualand West in 1878 a rebellion broke out and during the ensuing military operations he rose to major in command. The next year he was elected a member of the Cape Legislative Assembley for Aliwal North, a position he resigned in 1881 when the Cape government appointed him as its agent to take charge of the administration of Basutoland. Though he was partly successful in restoring order there, the Cape government returned the territory to British control in March 1883. Joseph then farmed in the Barkly East district, and from 1889 to 1896 represented Wodehouse in the Legislative Assembly. For many years he energetically promoted the South African fish industry, both in parliament and in the press. His suggestions in a letter to the Agricultural Journal of the Cape of Good Hope in July 1894 led to an investigation by the secretary for agriculture and recommendations to appoint a marine biologist (J.D.F. Gilchrist* was later appointed).
In 1896 Joseph moved to Rhodesia (now Zimbabwe) where he was appointed as surveyor-general on 9 July 1897, succeeding Andrew H.F. Duncan*. He also became a member of the Legislative Council (1899-1904) and served on the government's Executive Council from its inception in December 1898. In April 1902 he read a paper on "The diet of native labourers" before the Salisbury (now Harare) branch of the Rhodesia Scientific Association. The next year he retired (aged 75), returned to farming and conducted pasture experiments.
During his retirement Joseph wrote various newspaper articles and pamphlets on South African affairs, for example, policies relating to the indigenous population (1909), slavery (1910), drinking problems among indigenous people (1910, 1913), and temperance in South Africa (1915). These were published in East London, where he appears to have resided at this time. His Reminiscences of life in South Africa, from 1846 to the present day, with historical researches was published in Durban in 1908, and expanded in a series of articles in the Natal Advertiser in 1916. A combined edition was published in 1964. Joseph became a member of the South African Philosophical Society in 1900 and remained a member of its successor, the Royal Society of South Africa, until at least 1917. By 1910 he was a member also of the South African Association for the Advancement of Science. In 1916/7 he became a foundation member of the South African Biological Society. He has been described as adventurous, tough, versatile, exceptionally active, and intelligent.