John Beaver Marks joined the South African Communist Party (SACP) in 1928, at the age of 25. He was sent to the Soviet Union for the first time in 1930, as a student at the Communist University of the Toilers of the East (KUTV), as a result of funding from the Soviet Union in 1929. When he returned in 1933, he became the Communist party secretary. In 1934 rumours arose that he was a police informer and this may have been the reason he lost his position as party secretary in 1934-35. As supporter of party secretary Lazar Bach, who was recalled to the Soviet Union and killed there in 1936, Marks was also summoned to Moscow, but managed to bungle his exit and never arrived there.