George M. Clark qualified as Master of Arts (MA) at the University of Cambridge and was trained as an engineer at Messrs Crompton & Company in Chelmsford. He became an associate member (later a member) of the (Btitish) Institution of Civil Engineers. In 1894 he was appointed as assistant engineer to the Westminster Electric Supply Corporation and the next year became personal assistant to the chief engineer, Sir Alexander Kennedy. His main interest during his early professional years was in the measurement of temperature based on changes in the electrical resistance of metals. He reported this work in a paper read before the British Association for the Advancement of Science in 1894 entitled "On a direct reading form of platinum thermometer". Two other papers soon followed: "Note on the determination of low temperatures by platinum thermometers" (as joint author with E.H. Griffiths, Proceedings of the Cambridge Philosophical Society, 1895) and "The measure of temperature: An application of the measurement of resistance" (Electrician, 1897, in 5 parts),
On 12 August 1899 Clark succeeded A.P. Trotter* as Government Electrical Engineer (also named Government Electrician) in the General Post Office of the Cape Colony, a post he held for about three years. Also in 1899 he became a member of the South African Philosophical Society and was still a member of its successor, the Royal Society of South Africa, in 1917. He resided in Cape Town until 1903, when he moved to Johannesburg upon being appointed resident engineer to the Johannesburg waterworks, a post he held until 1907, when he became chief engineer to the Calcutta Electric Supply Commission.
In 1909 Clark returned to South Africa and acted as consulting engineer to the Victoria Falls and Transvaal Power Company. He was responsible for the company's compressed air system and for power station works. Subsequently he designed and oversaw the construction of power stations for Pretoria, Johannesburg and Bloemfontein. He joined the British Association for the advancement of science in 1902, and the newly founded South African Geographical Society in 1917. In 1917/18 he was president of the South African Institution of Engineers and in the latter year became a member of the South African Association for the Advancement of Science.
In October 1915 G.M. Clark, presumably him, gave an address at Naauwpoort, Cape Province, entitled "What is the Boy Scout movement?" The address was published as a pamphlet in Johannesburg that same year. In 1925 he retired and returned to England, where he served as a member of various committees of the British Standards Institution.