John Duncan Martin Derrett (more usually J Duncan M Derrett) (30 August 1922 – 21 October 2012) was Professor of Oriental Laws in the University of London, from 1965 to 1982, and afterwards Emeritus Professor.
Derrett was educated at Emanuel School, London, Jesus College, Oxford and the School of Oriental and African Studies, London and was called to the bar by Gray's Inn in 1953. He is the author of a number of works on law and the history of systems of law, India, religion (particularly Christianity) and comparative religion, latterly particularly of comparisons of Christianity with Buddhism. Derrett has also translated works by others into English.
Derrett appeared briefly in Dr Robert Beckford's television documentary The Hidden Story of Jesus (premiered on Channel 4 on 25 December 2007) discussing similarities between some Christian and Buddhist teachings and possible historical reasons for those similarities. With his "A Blemmya in India" (Numen Vol. 49, No. 4 (2002), pp. 460-474) Dr. Derrett met his Waterloo when surmising that "Blemmiya" were Africans, and Buddhists, in India.