During the Second World War Mackie served with the Royal Electrical and Mechanical Engineers in the Middle East and Italy, and was mentioned in dispatches. He was professor of philosophy at the University of Otago in New Zealand from 1955 to 1959 and succeeded Anderson as the Challis Professor of philosophy at the University of Sydney from 1959 to 1963. In 1963, he moved to the United Kingdom, becoming the inaugural holder of the chair of philosophy in the University of York, a position he held until 1967, when he was elected a fellow of University College, Oxford, where he served as praelector. In 1969, he gave a lecture, "What's Really Wrong with Phenomenalism?", at the British Academy as part of its annual Philosophical Lectures series. In 1974, he became a fellow of the British Academy.