Thomas Miller was discharged from the Royal Artillery at the Cape of Hood Hope on 31 July 1817 and received permission to remain in the colony. He left for London in January 1818, but returned to the Cape in January 1819. Presumably he is the same person as Thomas Miller who was a clerk to the Colonial Secretary, Sir Richard Plaskett, in the civil service of the Cape Colony until 1829, when he became aide-de-camp to the governor, Sir G. Lowry Cole. He collected plants around Cape Town and was acquainted with other local collectors such as J.L.L. Mund*, C.M. Villet*, and George Thom*. Miller corresponded with Dr W.J. Hooker, then Professor of Botany at Glasgow. In 1825 he sent Hooker a parcel of dried plants, collected by Villet on Table Mountain and the Cape Peninsula, followed by a second collection in 1827. In May 1827 he also sent Hooker a small parcel of plants collected by George Rex at Knysna.
Thomas Miller, of the Cape Civil Service, published a short monograph (40 pp) entitled Considerations on the exact position of the slave question (Cape Town, 1831) in which he appealed for the abolition of slavery. He may be the same person as Thomas Miller who died in 1839 and was the husband of Mary Ann Miller, born Rawlins.