Charles Ernest Randolph Mackesy was born in Dublin, Ireland, on 9 January 1861, the son of Captain Ernest Randolph Mackesy, formerly of the 97th Regiment of Foot, and his wife, Fanny Johnston Bell. His father had come to New Zealand after leaving his regiment, and had died at Auckland in October 1860. Mackesy was educated in France, Switzerland and Germany with the help of family members. He became an accomplished linguist and athlete. After moving to the United States, he married Jessie Adam in Dalis Peak, Kansas, on 30 November 1880.
Mackesy's father had acquired a 268-acre property near Whangarei; in the early 1890s Mackesy learned that this was about to be forfeited for non-payment of rates. Because things were not going well for him in the United States, he decided to come to New Zealand. This 'tall, well-built, pleasant man, with a notable American accent' managed to arrive just in time. Jessie and their three sons followed. The family developed the property into a successful farm and orchard. Gold was found at the back of the farm, but not in payable quantities.
Mackesy, a firm supporter of British-Israelism (he gave lectures on the subject throughout Australasia), believed that the United States and the British Empire would together win the great conflict which would inaugurate the millennium. Wishing to be prepared, he joined the Marsden Mounted Rifles as a trooper in 1900. A practical, resolute soldier and strict disciplinarian, within 11 years he had become lieutenant colonel of the 11th (North Auckland) Mounted Rifles (it was dubbed 'Nearly All Mackesy's Relations' after his sons joined up in 1914). Mackesy volunteered on the outbreak of the First World War, and left with the main body of the New Zealand Expeditionary Force as a lieutenant colonel in command of the Auckland Mounted Rifles Regiment, having secured adequate boots for his men by remonstrating with Prime Minister William Massey.
Mackesy landed at Gallipoli with his regiment in May 1915. He was soon sent back to Egypt to take charge of the New Zealand Mounted Rifles Brigade base, allegedly because he had on the same day both countermanded an order to cease firing and successfully opposed instructions to mount a suicidal attack. He was renowned for being outspoken and 'very quick at retort', attributes which probably contributed to his failure to become commander of the mounted brigade in 1917. His propensity for lecturing his men on the course of the war in the light of his interpretation of biblical prophecy may also have counted against him. He was, however, frequently in acting command of the Mounted Rifles during the Sinai–Palestine campaign of 1916–18.
Mackesy's courage and shrewdness in the field were often remarked on, as when he extricated a considerable body of men from an apparently hopeless trap in the desert by splitting them up and sending them galloping in different directions at prearranged intervals to confuse the Turkish gunners. In January 1917, when his regiment reached the Palestine border, he thanked God that he had at last been permitted to enter the Holy Land. By the end of that year his prediction of early 1915 that his men would spend Christmas 1917 in Jerusalem had been fulfilled.
Three times mentioned in dispatches, Mackesy was appointed a DSO and a CMG in 1917. On his return from leave in New Zealand in late 1917 he took charge of New Zealand training units and depots in Egypt. He served briefly as military governor of Salt and 'Ammān, east of the Jordan River, in late 1918, and remained for some months to advise the new Arab administration. Mackesy was made a CBE in 1919.
In late 1919 he resumed farming, and in 1921 opened an Auckland office of the land agency he had established before the war in Whangarei. Jessie Mackesy died in August 1920, and Charles returned to Whangarei, serving on the local county council and harbour board between 1921 and 1923. On 3 January 1925, at Auckland, almost 64, he married 37-year-old divorcee Miriam Lilla Davies. He unsuccessfully sought the Reform Party nomination for Marsden later that year.
On 20 November 1925 Mackesy died of heart failure at his home, The Hill, in Onerahi Road. 'Quite a gloom was cast over Whangarei'; flags flew at half-mast, and he was buried the following day with full military honours, after what an old friend described as a 'very disappointing funeral' for 'probably Northland's finest soldier'. He was survived by Miriam, and by his sons Charles and William. His other son, Harry, had been killed in August 1915 during the assault on Chunuk Bair. In 1943, 84 bush-covered acres of The Hill were purchased by public subscription and named Mackesy Park in his memory.