Royal Military Academy, Woolwich.
Arbuthnot was commissioned in the Royal Artillery on 17 February 1886. He later served in the Second Boer War in South Africa from 1899 to 1902, being mentioned in despatches. He was promoted to major on 28 October 1901, and in January the following year was appointed an assistant staff officer for colonial forces in South Africa.
By the time the First World War broke out he had risen to Lieutenant-Colonel and was Officer Commanding of the 44th (Howitzer) Brigade Royal Field Artillery, based at Brighton.
On mobilisation, the Brigade formed part of the artillery of the 2nd Division in the original British Expeditionary Force. Arbuthnot commanded the Brigade until May 1915, when he became Commander Royal Artillery of the newly formed 28th Division.
Although the Division spent only ten months on the Western Front before re-deploying to Salonika, it took part in several engagements at Second Battle of Ypres and in the Battle of Loos. Arbuthnot spent much of the rest of the war away from the Western Front.
He was Brigadier General, Royal Artillery of the XII Corps at Salonika from January to July 1916, Commander Royal Artillery of the 23rd Division in France and Italy from January 1917 to July 1918, and Brigadier General, Royal Artillery of the XXIII Corps, Home Forces, from July 1918 to the Armistice.
In World War I, he collected two medals and five clasps, being mentioned in despatches eight times, and being brevetted to command of the XII Corps in 1916. In the first years of the Second World War, he served with the Civil Defence. and was made an Honorary Brigadier-General in 1920. They had two children:
Major Sir Robert Dalrymple Arbuthnot, 6th Baronet (1919–1944)
Sir Hugh Fitzgerald Arbuthnot, 7th Baronet (1922–1983).