Robert Simpson was appointed Ensign on 15 Nov 1861 and commissioned Lieutenant on 5 Jan 1866, Captain with the 4th Foot on 15 Apr 1874, serving throughout the Abyssinnia Campaign, present at the action of Arogee and capture of Magdala, entitled to the Abyssinnia Medal.
Simpson was transferred to the Army Pay Department on 2 Dec 1878 with H.M.'s 4th Light Infantry and appointed Paymaster and Honorary Major with the Shropshire Light Infantry on 2 Dec 1883.