Mackie married Joan Meredith in 1947. One of their three children, Penelope Mackie, also became a philosopher. She lectured in philosophy at the University of Birmingham from 1994 to 2004, and was appointed Head of the University of Nottingham's Department of Philosophy in 2007. Mackie's son David is also a philosopher and graduated from Oxford University, where he held lectureships at Exeter College, Corpus Christi College, and Christ Church before being appointed a Fellow and Tutor at Oriel College. He is Head of Philosophy at D'Overbroeck's College, Oxford. Mackie's other daughter, Hilary, is a classicist at Rice University.