Heinrich S.D. Du Toit, son of Arie Gerhardus Jacobus du Toit and his wife, Martha Margaretha Maria, born Davel, received his schooling in Graaff-Reinet. In June 1894 he moved to the South African Republic (Transvaal), where he obtained a teaching certificate in September 1895. Subsequently he taught at the artillery training camp in Pretoria and qualified as an artilleryman, but during 1898 was a teacher at the S.P. van Wyk Botha Burgerschool in Pretoria. During the Anglo-Boer War (1899-1902) he served as a lieutenant in the State Artillery and was seriously wounded in the battle of Moddespruit, Natal. After recovering from his wounds he continued fighting until the end of the war in May 1902. He was promoted to captain and was wounded many more times.
After the war Du Toit went to the United States and qualified as a mechanic and agronomist in Peoria, Illinois. For a short time he was employed in the construction of the Panama Canal, but then visited various countries, including Russia, to study their agricultural practices. Upon his return to South Africa he was appointed as dry land agronomist in the Department of Agriculture of the Transvaal Colony in December 1908. After the formation of the Union of South Africa in 1910 he was appointed as dry land agronomist in the Department of Agriculture of the Union in October 1912. For many years he was in charge of the experimental station at Lichtenburg, but was later transferred to Pretoria. In 1916 he was appointed chairman of the Commission of Inquiry into Wheat, and in 1920 chairman of the Drought Investigation Commission. The latter commission recommended the paddocking system in stead of the widely practised kraaling of stock, for better control of grazing, and also made various recommendations aimed at improved soil conservation. Later Du Toit became head of the agricultural train that travelled around the country to promote scientific farming. By 1929 he was chief of the Division of Agricultural Education and Extension in the Department of Agriculture. He retired in October 1932.
Du Toit was the author of two semi-popular books, Drooge-land boerderij (also published in English as Dry land farming, Potchefstroom, 1913, 127 p) and Grondkonserwasie (also published in English as The conservation of our soil, Pretoria, 1929, 66 p). The first of these was aimed at farmers, the second at schools and the general public. In recognition of his contributions to agriculture he was awarded an honorary MSc (Agriculture) degree by the University of Stellenbosch in 1924. For some years he was a member of the councils of the University of Stellenbosch and the University of Pretoria. In 1909 he married Magdalena C.K.M. Hamman, with whom he had a son and two daughters.