After the outbreak of the Second Boer War in October 1899, a corps of imperial volunteers from London was formed in late December 1899. The corps included infantry, mounted infantry and artillery divisions and was authorized with the name City of London Imperial Volunteers. It proceeded to South Africa in January 1900, returned in October the same year, and was disbanded in December 1900. Wilson was appointed a lieutenant of the mounted infantry division on 3 January 1900, with the temporary rank of Lieutenant in the Army, and served as such until the corps was disbanded. He was present at the Relief of Kimberley and operations in the Orange Free State from February to May 1900, including actions at Karee Siding, Vet River (5 &amp; 6 May), Zand River. He was in the operations in the Transvaal in May and June, including actions near Johannesburg, Pretoria and Diamond Hill (11 June). He was again in the Transvaal, west of Pretoria, from July to 29 November, including actions at Zilikats Nek and Blands River (4–16 August), and operations in Orange River Colony in July. He was awarded the Distinguished Service Order and Mentioned in dispatches, and received the Queen's South Africa Medal with four clasps. He was granted the honorary rank of lieutenant in the army.