Patrick McGillewie emigrated from Atholl, Scotland, to South Africa in 1860, and became a Transvaal burgher in 1865, with a farm near Potchefstroom. There he organised trading and hunting expeditions into the interior. He also saw much military service, first joining "a Boer commando under Kruger to help the Orange Free State in a war against the Basutos." In 1874 he was in another commando "under President Burgess in a campaign against Sekukuni." He later served with Ferreira's Horse in another campaign against Sekukuni, was with the remounts department in the Zulu War, 1878, and then a member of the Border Light Horse under Major Carnforth.
He left the Transvaal in 1880, and returned to Queenstown, where he farmed. In 1896 he raised No. 1 Troop of the Queenstown Volunteer Mounted Infantry, being gazetted lieutenant, and in the ABW he served with the Queenstown Town Guard.
He was married to a daughter of Samuel Loxton, a former member of the Cape Assembly, and left a widow and three sons. No exact date of death given in British newspapers, but probably early to mid June 1911.