Commissioned a second lieutenant into the 9th Lancers on 10 October 1894, he was promoted to lieutenant on 25 September 1895. Kincaid-Smith was seconded for Colonial Office service in October 1898. When he returned from secondment he was back as a regular lieutenant in his regiment in January 1900, and served with the provisional Regiment of Lancers in South Africa during the Second Boer War. Following the end of the war in June 1902, he left Cape Town on the SS Canada and returned to Southampton in late July. He was promoted captain in 1903, but went on half-pay in 1904 due to ill health, and resigned his commission in 1908.
