Henry W. Piers was the son of Major Henry Piers, resident magistrate for Paarl until 1846, and his wife, Ann Rumbold. Henry was an amateur artist and self-taught geologist in the military establishment of the Cape Colony. He started his career in the Royal Engineers, Cape Town (1834-1839), and subsequently served in the Ordnance Department, Grahamstown (1840-1843), in Cape Town (1845-1846), as acting barracks master at Port Natal (now Durban, 1848), as deputy ordnance storekeeper and barracks master at Port Elizabeth (1849-1855), as acting barracks master at Fort Beaufort (1856-1858), in King William's Town (1859-1860), and again in Cape Town (1866-1868). During his peripatetic career he produced many drawings and paintings of scenes in the Cape Colony, including detailed topographical sketches, in pencil and watercolour. For example, a drawing of Stellenbosch (1835); a plan of the Castle in Cape Town (1838); a plan of Port Natal, showing the positions of British troops, Boer camps, landing places, roads, etc (1839); paintings of Port Elizabeth (1840, 1842); a drawing of the Rogge Battery near Cape Town (c. 1845); a drawing of Hof Street, Cape Town (c. 1850); and a drawing of the river wall at East London (1862). Copies of most of these works are in the Cape Town Archives Repository. In 1866 he requested the government of the Cape Colony to employ his son, Walter R. Piers*, and in 1870 requested employment for another son, Alfred H. Piers. He published two articles in the Cape Monthly Magazine (third series) titled "Kaffraria" (July 1871) and "The migration of Piet Retief and the Dutch Boers, beyond the Orange River, in 1836-1837" (November 1871).
Piers was active in the study of the geology and palaeontology of the Cape Colony for more that 20 years from about 1858. In May 1858 his "Rough notes on the geology of the immediate neighbourhood of Fort Beaufort" were published in the Eastern Province Monthly Magazine (Vol. 2, pp. 722-724), describing the sandstones and shales around the town and the fossils contained in them. The next year he presented a valuable collection of fossil fish, which had been obtained from a large block of sandstone near Fort Beaufort, to the Albany Museum in Grahamstown. The collection included two or three nearly complete individuals and represented the first fossil fish, except for some detached scales, found in the Karoo beds of the Eastern Cape. In addition he presented the museum with the skull of a Dicynodon fossil reptile and some other reptilian remains. Seventeen years later he added some more fossil reptile bones, also from Fort Beaufort, to the museum's collection.
In 1868 he described a "Fossiliferous deposit near Fort Grey in British Kaffraria" (South African Magazine, Vol. 2, pp. 217-218). He and George R. MacKay* had visited this calcareous deposit some 15 km west of East London and found that it contained much fossilised wood, which appeared to have been eroded out of older strata and redeposited. In the same volume of the journal, under the title "Discovery of extinct reptile bones in South Africa" (pp. 455-456), he gave a simplified account of a paper by T.H. Huxley* in the Geological Magazine, dealing with some fossils collected by A.G. Bain* and by MacKay.
After retiring from the military Piers remained in Cape Town. In October 1870 he was appointed acting curator of the South African Museum, mainly on the strength of his geological knowledge, when the curator, E.L. Layard*, left for England. He remained in the post until the appointment of Roland Trimen* in 1872. In 1870 he wrote a short paper on "The geology of Table Mountain" (Cape Monthly Magazine, Series 2, Vol. 1, pp. 253-255), in which he postulated, in disagreement with A.G. Bain* and others, that the Cape granite is of later origin than the Malmesbury slate and Table Mountain sandstone. The next year, in the same journal (Vol. 2, pp. 376-379), he replied to criticisms of the South African Museum, and contributed a paper "On the geology of the Cape Peninsula along the shores of False Bay" (Vol. 3, pp. 171-173). In 1874 he published a note on the Ribbon fish in the same journal. After the formation of the South African Philosophical Society in 1877, he contributed two papers to its Transactions, though he was not a member of the society: "The movement of sea sands and bar harbours" (1879, Vol. 1(1), pp. 7-11) and "Stray notes on the geology of Fort Beaufort district" (Vol. 1(2), pp. 23-26).
Piers showed some interest in prehistoric stone artefacts, but contributed little to their study. In a short article on "Stone implements" published in the Cape Monthly Magazine (September 1873, Series 2, Vol. 7, pp. 191-192) he expressed the belief that older so-called stone artefacts are actually naturally formed fragments, and refused to accept that humans could have existed contemporaneously with animals now extinct. Goodwin (1935) later described this contribution as "not helpful". Some stone artefacts were presented by Piers to the British Museum (Natural History).
During 1873 and 1874 H.W. Piers, presumably him, was an accountant in a Port Elizabeth bank and secretary of the Port Elizabeth Mechanics Institute (a voluntary organisation for the promotion of adult education). He married Ann Weakley at Grahamstown in 1842.