Stephen guest writes mostly on legal and political philosophy, particularly concerning the question of justification in legal reasoning and the relationship between justice, legal interpretation and laws. His well-known book Ronald Dworkin (Stanford UP) appeared in its third edition in 2012 and was reviewed by Tom Nagel in The New York Review of Books.  Amongst other work, he has published in Public Law on the role of the judiciary in revolutionary situations, the Law Quarterly Review on the logic of the law of hearsay evidence, the Journal of Medical Ethics  on the moral and legal rights of the subjects of medical research, and in Acta Juridica on both the ideas of de facto and de jure legislatures in Southern Rhodesia, in Pakistan, in Nigeria and Ghana. 

He has also written on the role of moral equality within legal reasoning, and in Revue Internationale de Philosophie on the idea that law is a form of justice, to which Dworkin has published a Reply.

In August 1998 he gave his father's 30th anniversary lecture - the F.W. Guest Lecture - at the University of Otago entitled 'Freedom and Status Revisited: Where Equality Fits In', which is published in the Otago Law Review 1999. His inaugural lecture, 'Why the Law is Just', was reviewed by Paul Johnson in The Spectator shortly afterwards, and is published in Current Legal Problems 2000. Johnson's criticism that treating people as equals is a dangerous idea contradicts his own acceptance - as a well-known Roman Catholic - that all people are equal in the eyes of God.

In 2002, he was appeared on the BBC's Radio 4 programme Unreliable Evidencechaired by Clive Anderson, with Lords Bingham and  Carnworth and John Gardner of the University of Oxford on the topic of the question whether there are legally right answers in appeal cases. He was alone in expressing the view that there were such answers on the ground that legal disagreement would make no sense if  it turned solely on questions of personal taste, a view Lord Bingham later described as 'bizarre'.  In 2009 he gave a public lecture at UCL entitled 'The Right to Obscene Thoughts' which was attended by several hundred sex workers, and resulted in his being nominated as Academic of the Year by the Erotic Awards Committee of the Leydig Trust.

Since 2008 he has published essays on the legality of the Pitcairn child abuse cases both for Oxford U.P. and the New Zealand Law Journal, on misinterpretation of Dworkin in Scott Shapiro's Legality in Analysis Reviews, on the objectivity of legal argument in Current Legal Problems, on how to criticise Dworkin's legal theory in Analysis Reviews, on Dworkin's Justice for Hedgehogs in Ethics and International Affairs, on the morality of the unity of law thesis in the Ukraine Law Review and on the Humean principle in law and morality in the Mexican journal Problema. He has recently written a Personal Note on Ronald Dworkin. In 2021 he submitted a critical commentary to the New Zealand government on its proposals for 'beefing up' hate speech crimes in the wake of the Christchurch massacre, now published in the New Zealand Law Journal, entitled 'Why Hate Has No Place in the Criminal Law'.