Hugh Clark qualified as Bachelor of Science (BSc) and became an associate member of the (British) Institution of Electrical Engineers (AMIEE). He came to South Africa shortly before the outbreak of World War I (1914-1918) to take up an appointment at the Durban Technical Institute (established in 1907). This institute became the Durban Technical College in 1915, and in 1922 the Natal Technical College (Durban), which operated under the wings of the Natal University College in Pietermaritzburg. In March 1923 Clark was appointed as the first professor of electrical engineering in Natal and became a member of the senate of Natal University College. During 1929-1931 Howard College was built in Durban and as soon as it was ready the engineering and commerce classes were transferred to it from the Natal Technical College.
During World War II (1939-1945) Clark agreed to train military recruits in the principles of electricity and radio technology and was given the rank of lieutenant-colonel. Under his leadership a department of radio-communication was established at Howard College, which became the training centre in radio for the whole of South Africa. The course was aimed mainly at graduate students and was started in 1942. Clark remained professor of electrical engineering until his retirement in 1954.
Clark's interest in the scientific enterprise as a whole is shown by a paper on "The aims and ideals of science", which he read in December 1918 and which was published by the Natal Society for the Advancement of Science and Art that same year. He became a member of the South African Association for the Advancement of Science in 1916. In 1921, and again in 1932, he served as joint secretary of Section A (which included engineering) when the association held its annual congress in Durban. During the 1932 meeting he presented two papers: "Note on a new type of continuously variable inductance of fixed resistance" and "Note on electrostatic capacity". As co-author with J. Roberts* he furthermore contributed to a paper on "The cost of generating and distributing electricity". All three papers were published in the South African Journal of Science (1932, Vol. 29). Years later he read a paper on "Transmission line phenomena at audio and radio frequencies" at a joint meeting of the Natal University College at Durban and the South African Institute of Electrical Engineers. His paper was published in the Institute's Transactions (1946, Vol. 37).