Charl (sometimes Carel) Daniel van der Merwe received his schooling at Wellington and passed the matriculation examination of the University of the Cape of Good Hope in 1898. The next year he passed the university's intermediate examination (equivalent to the first year of the BA degree) and then taught for a year at Barkly East and Wellington before continuing his studies at Victoria College, Stellenbosch. He was awarded the BA degree in science by the University of the Cape of Good Hope in 1906, then went to Germany for advanced studies in chemistry at the University of Halle, where he obtained a doctoral degree in 1909 with a thesis entitled Kondensation des Dicyans mit aromatischen Kohlenwasserstoffen.
After returning to South Africa van der Merwe was appointed in 1910 as a lecturer at Victoria College (from 1918 the University of Stellenbosch) and promoted to professor of chemistry in January 1911, a post he held until his death in 1946. He concentrated on inorganic chemistry and was an outstanding teacher who immediately created an interest in the subject in beginning students. He realised that chemistry lends itself to be treated as an exact science and taught this view successfully during a time when the subject was often still approached only from an empirical standpoint. Among his students he was affectionately known as 'Oubaas Carl'.
Van der Merwe was not known for his research. He and J.M. Joubert* wrote Introduction to inorganic preparations (Stellenbosch, 1918, 19 pp.) and later D.F. du Toit and he wrote Elementary chemistry for schools (1924), which also appeared in Afrikaans. During 1912 to 1915 he was an examiner in chemistry at the BA and MA level for the University of the Cape of Good Hope.
Van der Merwe was a member of the Suid-Afrikaanse Akademie vir Wetenskap en Kuns. In 1917 he became a member also of the South African Association for the Advancement of Science. He was married to Maria Johanna Kolbe, with whom he had two children.