Tomas Reeve worked as a civil engineer for Messrs Lucas and Aird in England for many years and was engaged on engineering works at, among others, the Royal Albert and Tilbury Docks on the Thames and the Alexandra Docks at Hull. Thereafter he was employed on the harbour works at Ensenada, Argentina. In 1888 he accepted a position with the Port Elizabeth Harbour Board. He was promoted to engineer-in-charge in 1900, and still held this position in 1905. He became a member of the Cape Society of Civil Engineers in 1904 and in 1913 was still a member of its successor, the South African Society of Civil Engineers. His hobbies were ornamental lathe work, microscopy, and natural history, and he served on the Port Elizabeth Museum Committee and the Port Elizabeth Library Committee.
By 1890 Reeve was a member of the Eastern Province Naturalists' Society and in 1908 represented that society on the King William's Town Museum Committee. He was a foundation member of the South African Association for the Advancement of Science (1902) and represented Port Elizabeth on its council during 1902-1905. In 1894 he donated some marine animals to the Albany Museum, Grahamstown. In 1917 he presented ants from Port Elizabeth to the South African Museum, Cape Town.