[5] Clarke served as Professor Emeritus of the History and Sociology of Religion at King's College London, having taught there from 1994 to 2003, the Director of the Centre for New Religions at King's College, and a professorial member of the Faculty of Theology at the University of Oxford (since 2003); earlier in his career (1974–1978) he was Professor of African History at the University of Ibadan, Nigeria.

[5][6] Clarke inaugurated a series of annual conferences on new religious movements at King's, which brought together academics from a variety of backgrounds.

Clarke and Byrne argued that "the various examples of religion will then be related by a network of relationships rather than shared possession of necessary and sufficient conditions for membership of the class."

[15] Clarke died on 24 June 2011, due to complications arising from deep-vein thrombosis.

[11] In view of his contributions to the field, a decision was made to retain his name as the editor of the Journal of Contemporary Religion until the end of the year 2011.