Thomas Williamson, soldier and plant collector, enlisted in the 72nd Regiment of Foot at Edinburgh in February 1825 and served in South Africa from October 1828 to April 1840. In December 1838 he was one of a small military force, commanded by Captain Jervis, sent to occupy Port Natal (now Durban). W.H. Harvey* employed him to collect plants in the Albany district of the Eastern Cape and in Natal during this expedition, probably with the consent of the commander of the regiment, Lieutenant-Colonel John Peddie, who was himself a plant collector. The force was called back to the Cape in December 1839.
In the Eastern Cape Williamson found a shrub which Harvey named Amphitalea williamsonii (Family Leguminosae) in his honor, but which has since been renamed. At Port Natal he probably collected the evergreen shrub on which Harvey based the genus Peddiea (Family Thymelaeceae). Harvey praised his intelligence and dilligence in the Flora Capensis (Vol. 2, 1862). His specimens are in the herbarium of Trinity College, Dublin.
Williamson was discharged from his regiment at Nenagh, Ireland, in July 1848, with the rank of sergeant.