 During the 1970s, Wijewardene worked as an expert on tropical farming systems with the UN Food and Agriculture Organisation (FAO) and the World Bank.He was head of agricultural engineering at the Mechanization and Automation Research Centre (MARDI) in Kuala Lumpur, Malaysia, from 1973 to 1974.He served as head of agricultural engineering and research at the International Institute of Tropical Agriculture (IITA) in Ibadan, Nigeria (1975–1980).