[3] He was principal researcher at the Klasies River Caves, one of the oldest known sites of anatomically modern humans, who lived there circa 125,000 years ago.
He then worked as an exploration geologist in Tanzania, Kenya, Ghana and the United Kingdom for six years.
[5] He was the recipient of a British Council Scholarship in 1967 that enabled him to attend University College, London, where he was able to gain experience in the preparation of pollen samples, charcoal and other organic material from archaeological sites.
He was the principal researcher at the well-known sites of Scott's Cave, Amanzi, Howiesons Poort, Wilton, Melkhoutboom, Highlands, Boomplaas and Matjes River, and latterly at Klasies River, one of the oldest known cave sites with well-preserved anatomically modern human remains dating from circa 115,000 years ago.
Deacon taught archaeology at the University of Stellenbosch and wrote over a hundred publications in journals, books, monographs and conference proceedings.