Birdwood served in the Second Boer War, initially as brigade-major with a mounted brigade in Natal from 10 January 1900 and then as Deputy-Assistant Adjutant-General on the staff of Lord Kitchener from 15 October 1900. Promoted to brevet major on 20 November 1901 and local lieutenant-colonel in October 1901, he became military secretary to Lord Kitchener on 5 June 1902, and followed him on his return to the United Kingdom on board the "SS Orotava", which arrived in Southampton on 12 July 1902. He received a brevet promotion to lieutenant-colonel in the South African Honours list published on 26 June 1902. In a despatch from June 1902, Lord Kitchener wrote the following about his work in South Africa: