Thomas Kirkman was the second son of Reverend T.P. Kirkman, and older brother of John Kirkmman, Natal businessman and politician. Thomas received his schooling at Rossall, Lancashire, and worked in various subordinate positions in Manchester for eight years. He came to Natal in September 1868 with his brother John and settled on government grant land some 70 km south of Durban, in Alexandra County. He served in the volunteer military force for 14 years and fought in the Anglo-Zulu War of 1879. In 1890 he was the honorary secretary arranging the Alexandra agricultural show. When responsible government was established in Natal in 1893 he was elected a member of the Legislative Assembly for Alexandra County. From 1898 until at least 1907 he was a member of the Legislative Council of Natal for Alexandra County. He resided at Esperanza, a few kilometers inland from the Natal South Coast, until at least 1916, and remained a bachelor.
Thomas's hobbies were coffee planting and microscopical studies. He was a member of the Quekett Microscopical Club (London), and in 1898 was elected a Fellow of the Royal Microscopical Society. At this time he began a study of rotifers, a group of microscopic, multicellular animals then popularly known as wheel-animalcules, which he obtained from fresh-water sources around Pietermaritzburg and Esperanza. He published two accounts of his observations in the Journal of the Royal Microscopical Society (1901, 1906), in which he enumerated 73 species. His work was familiar to the most prominent pioneer of rotifer research in southern Africa, the English authority Charles F. Rousselet*, who visited South Africa in 1905 and collected many rotifers for study, but left those of Pietermaritzburg and Durban for Kirkman's attention.
By 1906 Kirkman was a member of the South African Association for the Advancement of Science. That year Dr E. Warren*, director of the Natal Museum, named Bertramia kirkmani after him, a new species of protozoan found in a rotifer.