T. Holden Bowker was the fourth child of the 1820 settler Miles Bowker and his wife Anna Maria Mitford. Other scientifically minded members of the family were his brothers Octavius B. Bowker* and James Henry Bowker*, and his sister, Mrs Mary Elizabeth Barber*. Holden, as he was generally known, grew up in the Eastern Cape and was self-educated. He saw active service in 1828 against the M'fecani and served in the Sixth Frontier War (1834-1835) with the rank of lieutenant. Upon the death of his father in 1839 he inherited the family farm Tharfield, near Port Alfred, but was not successful as a farmer. During the Seventh Frontier War (1846-1847) he commanded a military post on the Fish River. In 1850 he served as magistrate in the Kat River Settlement, and during the Eighth Frontier War (1850-1853) was commandant of the burghers defending the settlement of Whittlesea. His heroic conduct during the fighting in 1851 led to the burghers presenting him with an award and testimonial. In 1853 he became the representative for Albany in the first Cape House of Assembly, and from 1858 to 1863 represented Victoria East. During these years he repeatedly tried to obtain compensation from the government for his services during the frontier wars. In 1855 he chaired the second meeting of the newly established Eastern Province Agricultural Association, at which its prospectus was adopted. The village of Queenstown was planned on his advice with an eye to defence. He was a member of the Land Board of Whittlesea in 1858 and commandant of the settlement by 1863. In 1872 he was secretary to the Land Commission on the New Rush Diggings at Kimberley. He was survived by his wife, Julia Eliza McGowan, and six children, including Mary Layard Bowker* and Miles McGowan Bowker*.
Holden was one of the first persons to recognise South African stone artefacts as the products of human action. At some time in 1857 or 1858 he visited E.L. Layard* at the South African Museum, who showed him some flint artefacts that had just arrived from Copenhagen. He recognised these as similar to stone points that he had picked up as a boy and had even used as arrow heads. On his return to the Eastern Cape he collected more of these artefacts at the mouth of the Kowie River and at nearby Kleinemonde and sent them to Layard. This was one of the first archaeological activities undertaken in southern Africa. The importance of the finds lies in Bowker's recognition that the artefacts were produced by humans, at a time when this idea was still a novelty even in Europe. When Layard received the package, the wife of Langham Dale*, Superintendent-General of Education, happened to be present and showed great interest. The finds may well have inspired Dale's own collecting of stone artefacts. Holden collected many more artefacts during the next number of years, many from beneath some metres of sand near the mouth of the Great Fish River, and he and Layard sent parcels of their finds to several persons in England. One set of 41 pieces was presented to the Royal Artillery Museum at Woolwich, London, in 1866. Others were sent to the Dublin Museum.
Holden's interest also included some other aspects of natural history. In 1867 he found several pieces of a human skull in a prehistoric grave marked by a flat stone near Tharfield. The remains were shown to the Albany Natural History Society by Dr. W.G. Atherstone*, who considered them to represent a young female. Towards the end of the next year Holden presented the curious cycad Stangeria eriopus, initially thought to be a fern, to the Society. Early in 1869 he presented five ducks, representing three species, to the Society, for its Albany Museum. In 1876 he donated a large male baboon to the museum, and at some time before 1883 some birds from Tharfield.