Cunynghame joined the Army in November 1830 after purchasing a commission as a Second Lieutenant in the King's Royal Rifle Corps, 60th Rifles. He was promoted to Lieutenant on 2 May 1835 and in 1841 was transferred to the 3rd Buffs. He served in the First Opium War as aide-de-camp to Major-General Alexander Fraser, Lord Saltoun, and he was present at the Battle of Chinkiang. He was mentioned in despatches and was present at the Treaty of Nanking. He served as aide-de-camp to Saltoun through January 1844. In 1845, he was promoted to Major and in November 1846 he was appointed Lieutenant-Colonel of the 13th Light Infantry. Within a month he transferred as Lieutenant-Colonel in the Grenadier Guards. He joined the 20th Regiment in 1849 and the 27th Regiment in 1852. In 1853–54, he served as aide-de-camp to his father-in-law, Commander-in-Chief of the ForcesViscount Hardinge, until returning to action in the Crimean War. In 1854, Cunynghame served as Assistant Quartermaster-General to the first division, and was present at the affair of Bulganac and was present at the battles of the Alma, Balaclava, Inkerman, Chernaya, and at the Siege of Sebastopol. He was mentioned in despatches, received the Crimean medal with four clasps, the Turkish medal, was appointed a légionnaire of the Legion of Honour, the third class of the Order of the Medjidie, and was created a Companion of the Order of the Bath. Cunynghame was promoted to the Brevet Colonel in June 1854 and to local Major-General in March 1855. Two months later he took command of a division of the Ottoman Army, receiving the personal thanks of Sultan Abdulmejid I, and was created a Lieutenant-General in the Ottoman Army. That October, he commanded 10,000 men to occupy Kerch, maintaining the position throughout the winter in the Crimea. He was upgraded to officier of the Legion of Honour and the second class of the Order of the Medjidie. He commanded an Infantry Brigade at Dublin from 1856–60, and then left for India, commanding forces at Bombay to 1862. He was promoted to major-general in 1861. He commanded the troops in Bengal from May 1862 to 1865, when he returned to Dublin, where he was in command of the Dublin District. In December 1868, was appointed Colonel of the 36th Regiment, succeeding the late Viscount Melville. In the 1869 Birthday Honours, he was created a knight commander of the Order of the Bath, and promoted to Lieutenant-General in 1870. From 1873–78, he commanded the forces at the Cape of Good Hope, serving through the Xhosa Wars in 1877, when he was appointed Lieutenant-Governor of the Colony. In 1878, he was upgraded to Knight Grand Cross of the Order of the Bath. In February 1876, he left the 36th Regiment to become Colonel Commandant of the 60th Rifles, his former Corps. On 1 October 1877, he was promoted to General. He was placed on the retired list in 1881.
Personal life
In 1845, he married Frances Elizabeth Hardinge, daughter of Henry Hardinge, 1st Viscount Hardinge. They had three daughters and two sons: Sir Henry Hardinge Samuel Cunynghame , a barrister, and Arthur Hardinge David Cunynghame. He died at sea returning home from India while traveling for pleasure with his eldest daughter.
