Kenneth Mackay, son of pastoralist Alexander Mackay, was born at Wallendbeen Station in 1859 and was educated at Camden College and Sydney Grammar. In 1885 he raised the West Camden Light Horse Regiment and later, in 1897, the Australian Volunteer Horse Regiment.
Mackay was a member of the New South Wales Legislative Assembly (1895-1899) and then the Legislative Council (1899-1900). He resigned from the latter to take command of the New South Wales 6th Imperial Bushmen's contingent for the Boer War in 1900, and served in Rhodesia and South Africa before returning to Australia in 1901. He took up a position in the Legislative Council again and remained there until 1934.
In 1906-1907 he was chairman of a Royal Commission covering the administration of Papua. The official report was published in 1907, and his own personal account, Across Papua, in 1909.
Too old for active military service in World War I he was appointed to raise an Australian Army Reserve from returned soldiers and was its first Director-General from 1916. He was awarded an OBE in 1920, and retired from the Australian Military Forces with the honorary rank of Major-General.