Leakey was born at Kabete in Kenya and educated at Cambridge University, where he studied French and Kikuyu. He held various academic posts at British and American universities, and was curator of the Coryndon Memorial Museum at Nairobi (1945–61). Apart from anthropological studies, notably of the Kikuyu people, Leakey is best known for his excavations of fossils of early humans, notably in Tanzania's Olduvai Gorge. Here, in 1959, jaw, skull, and huge teeth fragments of a species that Leadky called Zinjanthropus (Australopithecus) were uncovered by his wife Mary. The following year his son Jonathan discovered remains of the larger-brained Homo habilis. Both have been estimated at between 1,750,000 and 2,000,000 years old, but Leakey considered that only H. habilis was the true ancestor of modern humans, Zinjanthropus having died out: a view not shared by other researchers. Leakey also found, in western Kenya, remains of the earliest known hominid Proconsul africanus. Leakey's work has not only provided evidence for the greater age of humans but suggests that Africa, and not, as was previously thought, Asia, may have been the original center of human evolution.

Much of Leakey's work was carried out in close collaboration with his wife, Mary Leakey. She accompanied him on all his major field trips and worked alongside him as excavator, paleontologist, and author. She continued independent field work after her husband's death in 1972. In 1976, working in northern Tanzania in the Laetoli beds near Lake Eyasi, she made what she described as “the most remarkable find” of her whole career. Still preserved in the volcanic ash she discerned footprints of hominids, clear evidence that human ancestors had already adopted an upright posture some 3.75 million years ago. An account of her own researches was included in her autobiography Disclosing the Past (1984).