Born in Durban, Natal, on 14 October 1925, the only son and second child of Joseph Newman Tobias and Fanny Rosendorff, he received his first schooling in Bloemfontein and Durban. In 1945 he started his career as demonstrator in histology and instructor in physiology at the University of Witwatersrand. He received his B.Sc.(Hons) in Histology and Physiology in 1946-1947 and graduated in Medicine, M.B., B.Ch in 1950. He was appointed as a lecturer in anatomy in 1951. In 1953 he received his Ph.D. for a thesis entitled Chromosomes, Sex-Cells, and Evolution in the Gerbil. In 1955 he started his post-graduate research at Cambridge University, England where he filled the position of Nuffield Dominion Senior Traveling Fellow in physical anthropology. In 1956 at the University of Michigan at Ann Arbor and the University of Chicago he was the Rockefeller Traveling Fellow in anthropology, human genetics, and dental anatomy and growth.In 1959 he became Professor and Head of the Department of Anatomy and Human Biology, succeeding his mentor and eminent scholar, Professor Raymond Dart. In 1967 he was awarded a D.Sc. in palaeoanthropology for his work on hominid evolution. During this period he attended the University of the Witwatersrand. He was Dean of Medicine from 1980 to 1982. He was appointed Honorary Professor of Palaeoanthropology at the Bernard Price Institute for Palaeontological Research in 1977 and Honorary Professor in Zoology in 1981.

Tobias has excavated at the Sterkfontein caves and worked at almost all other major sites in Southern Africa since 1945. He has also opened some 25 archaeological sites in Botswana while on the French Panhard-Capricorn Expedition while conducting a biological survey of the Tonga People of Zimbabwe. He was one of the anthropologists instrumental in unmasking the Piltdown fraud.

His research has been mainly in the fields of paleoanthropology and the human biology of African people. He has studied the Kalahari San, the Tonga people of Zambia and Zimbabwe and numerous black races of Southern Africa. Phillip Tobias is best known for his research on hominid fossils and human evolution, having studied and described hominid fossils from Indonesia, Israel, Kenya, Namibia, South Africa, Tanzania, Zimbabwe and Zambia. His best known work was on the hominids of East Africa, particularly those of the Olduvai Gorge. Collaborating with Louis Leakey, he identified, described and named the new species Homo habilis. Cambridge University Press published two volumes on the fossils of Homo habilis from the Olduvai Gorge. He is closely linked with the archaeological excavation at the Sterkfontein site, a research programme he initiated in 1966. The Sterkfontein cave has seen the most sustained excavation of a single site in the world. This site has yielded the largest single sample of Australopithecus africanus as well as the first known example of Homo habilis from Southern Africa. It is now a world heritage site.

He is one of South Africa's most honoured and decorated scientists, and a world leading expert on human prehistoric ancestors; he has been nominated three times for a Nobel Prize, received a dozen honorary doctorates and been awarded South Africa's Order for Meritorious Service.

Tobias has published over 600 journal articles and authored or co-authored 33 books and edited or co-edited eight others.He has received honorary degrees from seventeen universities and other academic institutions in South Africa, the United States of America, Canada and Europe. He has been elected as a fellow, associate or honorary member of over 28 learned societies. These include being elected a foreign associate of the National Academy of Sciences (USA) and a Fellow of the Royal Society of London. Among the very many medals, awards and prizes he has received are the Balzan Prize for Physical Anthropology (1987) and the Charles R. Darwin Lifetime Achievement Award of the American Association of Physical Anthropologists (1997). The Royal Society of South Africa is very sparing with its honours, and Tobias is one of only two South African Honorary Fellows of the Society and one of very few recipients of its senior medal, the John Herschel Medal.

He holds the positions of Professor Emeritus of Anatomy and Human Biology at the University of the Witwatersrand, Honorary Professor of Palaeo-anthropology, Honorary Professorial Research Associate and Director of the Sterkfontein Research Unit, and Andrew Dickson White Professor-at-Large of Cornell University, Ithaca, New York USA. He has been a visiting professor at the University of Pennsylvania, University of KwaZulu-Natal, Cambridge University and other institutions. He has taught over 10 000 students during his fifty years of service at Wits Medical School.

He was an outspoken critic of institutionalised apartheid and campaigned actively for its abolition.