William John Lamont, agriculturalist and farmer, was the son of Peter Lamont and his wife Isabella Maria Morrison Lamont, born Glennie. He matriculated through the University of the Cape of Good Hope in 1900 and entered the civil service of the Cape Colony on 1 January 1901, and again on 1 January 1903, in a temporary capacity. In 1904 he received a permanent appointment in the Department of Agriculture. However, during 1904-1905 he was also enrolled as a student at the South African College, Cape Town, though he did not obtain a formal qualification. On 1 September 1909 he was appointed as agricultural assistant and by the next year was acting government agriculturalist. At that time he was stationed at the Department's School of Agriculture at Elsenburg, near Stellenbosch (later the Stellenbosch-Elsenburg College of Agriculture). He conducted some fertiliser experiments to assess the relative rust resistance of wheat and oats, obtaining positive results with superphosphate and basic slag, but not with potash. The results were written up in "Manuring of wheat in the Caledon district" (Agricultural Journal of the Cape of Good Hope, 1910, Vol. 37(1), pp. 243-248) and "Experiments with wheat varieties in the Cape Province, 1910" (Agricultural Journal (Union of South Africa), 1911, Vol. 2, pp. 305-309).
In 1911 Lamont was appointed acting principal of the Grootfontein School of Agriculture, near Middelburg. He no longer held this position by 1914, but was still (or again) associated with the school in 1918. In 1920 he was promoted to principal of the School of Agriculture at Elsenburg, a position he held until 1925. He visited the United Kingdom and the United States of America in 1923, and in 1928-1929 undertook a journey to the United Kingdom, continental Europe and South America. During the period 1928-1933 he conducted tobacco investigations and represented tobacco growers in a deputation to the United Kingdom. During these years he also wrote Review of the maize situation in South Africa (Pretoria,1931). In 1933 he was appointed under secretary in the Department of Agriculture, and later that year became secretary of the new Department of Commerce and Industries.
Lamont joined the South African Association for the Advancement of Science as a member in 1916 and two years later was elected a member of its council, representing Middelburg. He was married to Johanna Susanna ("Joey") Nienaber, with whom he had four sons.