Adolphus Peter Elkin was born in West Maitland, New South Wales on 27 March 1891. Elkin was raised by his maternal grandparents following the divorce of his parents in 1901 and death of his mother in 1902. Educated in Singleton and at Maitland East Boys' High School, Elkin began his career as a bank clerk before entering St Paul's College at the University of Sydney to study theology (B.A., 1915; M.A., 1922).

After being ordained as an Anglican priest in 1916, Elkin served in this role in small country parishes around Newcastle until becoming a full time teacher at St John's Theological College in Armidale from 1919. It was in 1918 that a visit to the outback near Bourke sparked an interest in Australian Aboriginal societies. Completing his master's thesis on the religion of Australian Aboriginal people, Elkin lectured on early society and culture and the origin of humans. Elkin went on to complete his Ph.D in 1927 at University College, London.

Following his return to Australia, Elkin secured a Rockefeller grant to undertake field work in the Kimberley, Western Australia. Returning to New South Wales in 1928, Elkin took a position as rector of Morpeth, where he was supported to follow his anthropological interests and began advocating for what he believed was social justice for the Aboriginal people of Australia. Elkin began publishing in academia and popular media, as well as speaking throughout New South Wales on the topics of race relations, prejudice, justice and citizenship for Aboriginal Australians.

Returning from field work in South Australia, Elkin took over as professor of anthropology at the University of Sydney. As the predominant voice in Australian Anthropology, Elkin advised government, edited Oceania and served as director of field research through the Australian National Research Council's anthropological committee (1933-42; executive member of ANRC 1942-55 & chairman 1954-55). Elkin also served as president (1933-62) of the Association for the Protection of Native Races and vice-president of the Aborigines Protection Board of New South Wales (Aborigines Welfare Board from 1940).

Elkin was president of the Anthropological (1934) and Royal (1940-41) societies of New South Wales, the Australian Anthropological Association (1941) and the Australian Institute of Sociology (1941-44); he was a fellow (from 1937) of the Australian and New Zealand Association for the Advancement of Science, Australian councillor (from 1947) on the Pacific Science Association, a fellow (from 1953) of the Social Science Research Council of Australia, a founding councillor (1961) of the Australian Institute of Aboriginal Studies, a trustee of the Australian Museum, Sydney and a member of the Royal Empire Society.

Following his retirement in 1956, Elkin served as chairman of St Paul's College council and remained prominent in Anthropological circles, editing Oceania until his death and serving as a foundation editor (1966-79) of Archaeology & Physical Anthropology in Oceania. Elkin was awarded the local Royal Society's James Cook medal (1956), Australian and New Zealand Association for the Advancement of Science's Mueller medal (1957), and the Herbert E. Gregory medal (1961); he was appointed C.M.G. in 1966 and in 1970 received an honorary doctorate of letters from the University of Sydney. Elkin continued to write while living at Mowll Memorial Village until his death in 1979.