Okali is former president of the Nigerian Academy of Science and emeritus professor of forestry at the University of Ibadan, Nigeria and chairman of the Nigerian Environmental Study/Action Team at Ibadan. He was previously chairman of the National Committee of UNESCO's Man and the Biosphere Programme. He obtained a PhD in plant ecology from Sheffield University, United Kingdom, in 1964, read forestry at Oxford University, and worked as a lecturer mostly at the University of Ibadan until his retirement in 2001. He was also a visiting professor at Yale in 1983 and 1987 and Yamani fellow at the University College of North Wales, 7 Bangor, in 1988. He is a fellow of the Nigerian Academy of Science and member of the New York Academy of Sciences.