His father was Major General Arthur FitzRoy Hart-Synnot and his uncle, Sir Reginald Hart, was awarded the Victoria Cross in Afghanistan.

[4] After passing out from the Royal Military College, Hart-Synnot (then Hart) was commissioned into the East Surrey Regiment as a second lieutenant on 8 October 1890.

[5] He was promoted to lieutenant on 7 June 1892,[6] and served with the Chitral Relief Force under Sir Robert Low in 1895 in command of the Maxim gun detachment of the ist Battalion East Surrey Regiment (Medal with Clasp).

Hart served in the Second Boer War from late 1899, first in command of the Northern Company of Mounted Infantry, being present during all the operations about Naawpoort and Colesberg with French's Cavalry Division (for which he was mentioned in despatches).

[7] Following the end of the war in June 1902, Hart returned to the United Kingdom on the SS Soudan, arriving at Southampton in early September.

[23] The following year, he was appointed a Companion of the Order of St. Michael and St. George (CMG) in a special addition to the 1919 Birthday Honours.