St Vincent W. Erskine was a son of Lieutenant-Colonel David Erskine (1816-1903), Colonial Secretary of Natal for many years, and his wife Anne Maria, born Spode. He arrived in Natal with his parents in 1858 and entered the Natal civil service in March 1868 as a treasury clerk in Pietermaritzburg. However, in May that year he answered the call of adventure and travelled to the Transvaal where he met Karl Mauch* at Lydenburg. From there he journeyed north and eastwards to the junction of the Olifants River with the Limpopo, then followed the latter to its mouth, which he reached in September despite the opposition of local chiefs. Early in 1869 he was back in Pietermaritzburg, employed as second clerk in the office of the Surveyor-General. That same year his first paper, "Journey of exploration to the mouth of the river Limpopo", with a map, was published in the Journal of the Royal Geographical Society (Vol. 39, pp. 233-276), of which he was elected a Fellow. At this time he also produced a pamphlet on The South African diamond fields (Durban, 1870), which propagated the route via Natal, rather than via Port Elizabeth, to the diamond fields near Pniel on the Vaal River. In 1870 he was elected a member of council of the Natural History Association of Natal, serving until the association ceased to function a few years later. In August that year he read a paper before the association on "The tsetse fly (Glossina morsitans)". It was published in Durban that same year. Another short paper by him, "Meteorology at Natal", was published in Nature (London, Vol. 4, p. 305) the next year.
In 1871 the Lieutenant-Governor of Natal sent Erskine on a mission to King Mzila of Gazaland. He sailed from Durban to Delagoa Bay (now Baia de Maputo), but the Portuguese governor refused him permission to travel inland. Sailing on to Inhambane he entered Mzila's territory from there and during an extended stay spent much time in geographical exploration. He travelled south to the lower Limpopo, and then north along a different route to Mzila's capital on the slopes of the Chimanimani Mountains (on the Zimbabwe-Mozambique border), which he reached in April 1872. After returning to Natal he explored a section of the Limpopo immediately above its junction with the Olifants and then followed the latter upstream for some distance before turning south to Lydenburg. He reached Natal again in October 1872. An account of this second journey, "A journey to Umzila, in South-Eastern Africa, 1871-2", was published in the Journal of the Royal Geographical Society (Vol. 45, pp. 45-127) in 1875.
In 1873 Erskine started his third journey to Gazaland, proceeding to Inhambane, then up the Sabi (Save) River and on to Mzila's capital. After exploring the upper Sabi he travelled down this river to its mouth and explored the coast northwards from Chiluane to the mouth of the Gorongosi before turning south to Inhambane. He was back in Natal in June 1874, but in August that year started his fourth journey. This took him mainly to the area south of the Sabi River, where he hunted and explored from November 1874 to June 1875. His paper, "Third and fourth journeys in Gaza, or southern Mozambique, 1873 to 1874, and 1874 to 1875" was published in the Journal (Vol. 48, pp. 25-56) in 1878. The account of the fourth journey was written up from his journal by Dr R.J. Mann*. The paper included Erskine's astronomical observations and tables of latitudes.
Erskine's four journeys contributed significant new information on southern Mozambique. He described the natural features of the country, its game and human inhabitants, the navigability of the Limpopo, and the position of the Zimbabwe ruins.
In February 1876 he moved to East Griqualand as a surveyor. During the Griqua uprising early in 1878 he was injured while staying in Kokstad with his family. He still resided in Kokstad in 1884, but by 1892 had moved to the Transvaal and was living in Standerton. He was admitted as a land surveyor in the Transvaal and worked for the government in that capacity. His earlier determination of the latitude and longitude of Lydenburg was listed in the Transvaal book almanac and directory for 1881. By 1895 he worked as a mining engineer in Johannesburg. He joined the Institute of Land Surveyors of the Transvaal, which was incorporated by an act of parliament in 1904, and in the first issue of its Journal in 1905 is listed as a member living in Johannesburg. In 1909 he was working as a surveyor in Zululand, but then moved to the Cape Province where he was licensed in 1913.
In 1870 Erskine married Alice Lindley Buchanan, with whom he had six children. They later settled in Cape Town where he died of the Spanish flu in 1918.