He became interested in natural history as a child, facilitated by the California Academy of Sciences in Golden Gate Park, which was near his family home.
Working with Robert Heizer, his PhD dissertation examined the prehistoric archaeology of Surprise Valley, California.
There he undertook ethnoarchaeological work with Alyawarra and Anmatjere speakers (dialects of Arrernte) near Bendaijerum station in the Northern Territory of Australia.
Since arriving at Utah in 1978, O'Connell has continued to undertake ethnoarchaeological and archaeological research in Western North America and Australia.
Collaborating with Kristen Hawkes and Nicholas Blurton Jones, research has sought to explain the evolution of human life histories,[7] Plio/Pleistocene hominid hunting strategies[8] and the emergence of the genus Homo[9] from an evolutionary ecological perspective.