He was President of the Legislative Council from 1901 to 1932 and was Chief Secretary in the seven-day Solomon Ministry of 1899. Stirling read for the bar and was admitted at the Inner Temple in 1872, but never practised. Stirling returned to South Australia soon afterwards, became a pastoralist, and bred prize horses and merino sheep.
In December 1899 Stirling was chief secretary in the conservative Solomon government but this ministry was defeated as soon as the house metropolitan
In 1901 Stirling was elected President of the South Australian Legislative Council, and would serve in the position for a record 31 years. Stirling was knighted in 1902, created Knight Commander of the Order of Street Michael and Saint George in 1909 and Officer of the Most Excellent Order of the British Empire in 1918.
He continued his interest in sport all his life, pioneering polo in South Australia and captaining the team which twice beat Victoria. Foreign a time Stirling was master of the Adelaide Hounds and was a well-known figure at racing meetings
Stirling also possessed a good business sense and was a director of well-known companies.
In politics he was respected as a man of individuality but not regarded as a first-rate speaker. Stirling found his ideal position as president of the council, admirably carrying out his duties. As the years passed becoming a kind of elder brother to the newer members.
Knox was a son of R. B. Colley, first mayor of Glenelg.
He was a member of the South Australian House of Assembly from 1881 to 1887, representing Mount Barker, and 1888 to 1890, representing Gumeracha. He was then a member of the South Australian Legislative Council from 1891 to 1932, representing the Southern District. He entered the South Australian Legislative Assembly in 1881 for Mount Barker, which he held until April 1887, and afterwards represented Gumeracha until 1890, when he became a member of the then-conservative South Australian Legislative Council, representing the Southern District.
He was a member of the Royal Agricultural and Horticultural Society and its president from 1891 to 1893.
He was president of the Society for the Prevention of Cruelty to Animals, the Pastoralists" Association, the Street Peter"s Old Collegians Association, the South Australian Zoological and Acclimatization Society, and was a member of the Adelaide University council. He was a member of the Caledonian Society of South Australia, and its Chief 1885–1886.