Holness was born in Jamaica and moved to Canada where he completed his BSc at McGill University and his doctorate in Physiology at University of Western Ontario. His research afterwards would branch into diving and aerospace medicine. As a result of his research, the Canadian military saw improved technologies especially for divers and pilots of high-performance aircrafts. Holness was a group leader in the Defence Research Lab and Canadian Project Officer and Representative to NATO Advisory Group for Aerospace Research and Development.
At the Department of National Defence headquarters, Holness was responsible for monitoring research programs, including occupational health and aerospace medicine. He also assessed Canadian participation in international defence research and development programs. Between 1988 and 1992, Holness was the Scientific Liaison Officer at the Canadian Embassy in Washington after which he returned to the Department of National Defence headquarters in 1992 where he retired three years later.