[1] Renwick then returned to Sydney in 1862, living in Redfern[1] where he established a rapidly growing practice, becoming eventually one of the leading physicians and the first president of the local branch of the British Medical Association.
[1][5] He became Secretary for Mines in the third ministry of Sir Henry Parkes on 12 October 1881, but lost his seat at the election held in December 1882.
[6] He was elected for Redfern in October 1885,[7] and was Minister of Public Instruction in the ministry of Sir Patrick Jennings from 26 February 1886 to 19 January 1887.
Renwick authored the Benevolent Society's incorporation act, he founded the state children's relief department, and as president of the original committee he had much to do with the bringing in of old-age pensions in New South Wales.
He was an early advocate for the foundation of a medical school at the university, and in 1877 donated £1000 to found a scholarship in the faculty of medicine.