Charles John Marc Constancon was a lecturer in the Department of Mathematics at the South African School of Mines and Technology (from 1922 the University of the Witwatersrand), Johannesburg, from 1917 to his retirement in 1945. The department's main function during these years was to provide courses in mathematics for engineering students. Constancon's only known publication is a paper entitled "A power factor diagram", published in the Transactions of the South African Institute of Electrical Engineers (1915, Vol. 6(12), p. 332). He became a member of the South African Association for the Advancement of Science in 1917.
Constancon has been described as "a colourful personality" (Murray, 1982, p. 155). He was married to Thelma Cecilie Hansen, born Mickdal, with whom he had two sons. After they were divorced in 1931 he married Helene Letitia McIntosh, who survived him.