William Craig was educated at King's College, Aberdeen, and obtained engineering experience in the United States and Australia before coming to the Cape Colony in 1893. He was an associate member (later a member) of the (British) Institution of Civil Engineers and a member of the Society of Engineers, London. In South Africa he was employed as an assistant engineer in the Public Works Department, Cape Town, from December 1893. In October 1904 he became first engineer in the Irrigation Branch, but on 1 July 1906 returned to the Public Works Department as chief engineer. He retired from this post on 1 January 1909. At that time he resided in Oranjezicht, Cape Town. In about 1901 he reported to the government of the Cape Colony on water boring and other engineering works in Australia and in 1906 he and Prof Henry Payne* reported on schemes for conserving the water flowing from Table Mountain. Among others he drew up plans for the water supply of Porterville in 1914.
Craig served on the first committee of the Cape Society of Civil Engineers, founded in Cape Town in January 1903, and was again a committee member in 1904 and in 1907. Although he was no longer a member of the society by 1909, he served as president of its successor, the South African Society of Civil Engineers, in 1919. He joined the South African Philosophical Society in 1901 and was still a member in 1907. He was also a foundation member of the South African Association for the Advancement of Science in 1902. At the Association's first meeting in Cape Town in 1903 he read a paper on "Curved concrete reservoir walls..." (Report, 1903, pp. 404-408). The paper was based on a visit he had recently made to Australia, where curved concrete reservoir walls had been built since 1900 by the Public Works Department of New South Wales, following earlier experience in the United States and elswhere. Given the correct circumstances (e.g., a narrow rocky gorge) these walls were a suitable replacement for gravity sections. None had yet been built in South Africa at this time.