Stephen guest is Emeritus Professor of Legal Philosophy at University College London (UCL). He graduated in Philosophy (1971) and Law (1973) from the University of Otago in New Zealand, receiving the New Zealand Butterworth Prize in Jurisprudence, and taught Logic for two years in the Otago Philosophy Department before studying with Ronald Dworkin at University College, Oxford. With Jo Wolff of the UCL Philosophy Department, he co-chaired with Dworkin the distinguished and internationally well-known annual Colloquia in Legal and Social Philosophy at UCL from 1999 to 2006 (see End of a Golden Era?) He was also staff editor until 2008 of the UCL Jurisprudence Review, the student edited law journal he founded in 1994. A Barrister and Solicitor of the NZ High Court, and Barrister of the Inner Temple, he was a tenant at 199 Strand, London, from 1993 to 2005. Significant opinions he wrote were for the defence in the Privy Council of the NZ multiple murder case of Bain (1996) and for the Public Defender in the Pitcairn Island sexual abuse case of Fletcher & Others (2006) at all levels including the Privy Council.

In 1987, he was Visiting Scholar at New York University Law School and a visiting researcher at Harvard Law School. He was again Visiting Scholar at NYU for 1996. In both 2005 and 2006, he was Visiting Professor in Jurisprudence in the Otago Faculty of Law. He was a British Academy/Leverhulme Senior Research Fellow for 2006-2007. In 2013 he was Visiting Professor at the University of Namibia Law School, and in 2017, Visiting Professor at the law school of Macau University.

At UCL, he was Sub-Dean and Faculty Tutor (1980-85), Secretary of the Bentham Club (1980-85), Secretary to the Bentham Committee (1982-87), Vice-Dean and Deputy Head of Department (1993-1995), Convener of the MA in Legal and Political Theory (1995-2000) in the Department of Political Science, Director of Laws Research Students (2004-2006), and Legal Member of the UCL & Hospital Research Ethics Committee (1985-1999). For two decades he was the Convener of both the UCL LLB and University of London LLM programmes in Jurisprudence, and the Convener and Chief Examiner for the University of London International LLB and LLM in Jurisprudence. For 12 years he was also the Convener and Chief Examiner of the Law of Evidence for the London International LLB. From 1993 - 2006 he was Advisory Professor for the London International LLB at the Kemayan Advanced Tutorial College in Kuala Lumpur. He wrote subject guides for both Evidence and Jurisprudence for the London International degrees. In 2001, UCL awarded him the distinguished teaching award for the Faculty of Laws and, in 2011, the Stephen Guest Writing Prize was instituted by the UCL law students to mark the best writing in Jurisprudence within the Faculty. Eight of his successful PhD students are in permanent academic posts around the world.

He plays the violin and was formerly a founder member of the Dunedin Civic Orchestra, a violinist in the New Zealand National Youth Orchestra for seven years, an active member of the Dunedin Opera Company, and was twice a finalist in the NZ Chamber Music Federation competition. He was President of the OUSA Music Union 1968-1971 and Board member of the Dunedin Chamber Music Society. He was also a violinist in the Oxford University orchestra, the University College Oxford orchestra, UCL opera and orchestra, and others. He has performed many times in London at the UCL & Hospital Chamber Music Society.

His other main interests are painting, for which he won a prize at the NZ Universities Arts Festival in 1968 - Wind, Trees, Insects - and hunting deer on the West Coast of New Zealand.