Constantine is Professor of Philosophy at the University of Hertfordshire, Director of Lex Academic and a Fellow of the RSA. He describes his philosophical interests as "unfashionably broad, but I work primarily in the philosophy of action, moral psychology, and interpersonal understanding. I also have an interest in the psychology of philosophy, as advanced by Hume, Nietzsche, and Wittgenstein." He spent most of his twenties as a theatre director and playwright. Constantine writes a quarterly opinion column for The Philosophers' Magazine, contributes to Times Higher Education and The Times Literary Supplement, and frequently appears as a guest on radio programmes such as The Moral Maze, Analysis, and Free Thinking.
Constantine is vegan and has a naturalistic worldview.