Darling seems to have been unique in the British Army of this period, as he progressed from an enlisted man to become a general officer with a knighthood. Born in Ireland, he was the son of a sergeant in the 45th Regiment of Foot who subsequently gained the unusual reward of promotion to officer rank as a lieutenant. Like most of the small number of former non-commissioned officers in this position, Lieutenant Darling performed only regimental administrative duties. He struggled to support his large family on a subaltern's pay.