After his education at Haileybury, Ian Bonham-Carter was commissioned into the Northumberland Fusiliers in 1900. Bonham-Carter served in the 5th Battalion and then the 1st Battalion of the Northumberland Fusiliers before being appointed adjutant in 1909. In May 1914 he attended No 6 Course at the Central Flying School, receiving his Aviator's Certificate no. 794 on 25 May 1914. After completing his flying training, Bonham-Carter served in the Royal Flying Corps until he transferred to the RAF on its creation in 1918.