Fuller was commissioned into the 1st Battalion of the Oxfordshire Light Infantry (the old 43rd Foot), and served in South Africa from 1899 to 1902. In the spring of 1904 Fuller was sent with his unit to India, where he contracted typhoid fever in autumn of 1905; he returned to England the next year on sick-leave, where he met the woman he married in December 1906. Instead of returning to India, he was reassigned to Volunteer units in England, serving as adjutant to the 2nd South Middlesex Volunteers (amalgamated into the Kensingtons during the Haldane Reforms) and helping to form the new 10th Middlesex. Fuller later claimed that his position with the 10th Middlesex inspired him to study soldiering seriously. In 1913 he was accepted into the Staff College, Camberley, starting work there in January 1914.