Louis Phillpotts received his first commission as a second lieutenant in the Royal Artillery on 14 February 1890, and was promoted to the rank of lieutenant on 14 February 1893. He served during the Second Boer War, between 1899 and 1901, where he fought in the Battle of Modder River (November 1899) and took part in the Relief of Kimberley in February 1900. He was promoted to the rank of captain on 23 January 1900, and served as a divisional adjutant in South Africa in 1901. Promotion to the rank of major followed on 3 July 1907. He served during the First World War, was promoted to the rank of lieutenant colonel in October 1914, and to the rank of brigadier general in 1915.