Broom was first known for his study of mammal-like reptiles. After Raymond Dart's discovery of the Taung child, an infant australopithecine, Broom's interest in paleoanthropology was heightened. In 1934 Broom joined the staff of the Transvaal Museum in Pretoria.
In the following years, he made a series of spectacular finds, including fragments from six hominids in Sterkfontein, later classified as an adult australopithecine, as well as more discoveries at sites in Kromdraai and Swartkrans. In 1937, Broom made his most famous discovery--an Australopithecus robustus. These discoveries helped support Dart's claims for the Taung species. The remainder of Broom's career was devoted to the exploration of these sites and the interpretation of the many early hominid remains discovered there.