D'Aguilar was an ensign in the 86th Regiment in 1799 and served eight years in India. In Europe, he saw active military service in the Walcheren Campaign, the Levant, Spain and Greece. From 1823 he was assistant Adjutant-General at the Horse Guards and for 11 years, deputy Adjutant-General in Dublin. In 1841 he was promoted to Major-General and appointed to command the northern district in Ireland. In 1843, he was appointed to control of the garrison in Hong Kong which had then only been ceded to Britain by China two years previously and had additional responsibility for the troops stationed under the Treaty of Nanking of 1842 at Chusan [Zhoushan] and Amoy [Xiamen]. At the same time, he was given commission as Lieutenant-Governor of Hong Kong. In April 1847, he sailed with an expeditionary force to attack Canton [Guangzhou]. D'Aguilar handed over his command to General Staveley in Feb. 1848. He was knighted in 1852. In 1853 he wrote 'Pencillings on the Rock' but this was never published and he died in London in 1855.