[2] Kelly’s early work and main contribution as a historian of political theory was as part of a group of revisionist Bentham scholars, having worked on the manuscripts at the Bentham Project at University College London.

Kelly rejected the common claim that Bentham was a crude act-utilitarian.

His work on the book Political Thinkers, edited with David Boucher, has defended a non-contextualist approach to past political thinkers in contrast to the linguistic contextualism defended by Quentin Skinner amongst others.

His criticism of multicultural theories and communitarianism, has led to a defence of liberal egalitarianism that draws on the work of British political theorists such as Brian Barry and H. L. A. Hart, as much as that of John Rawls.

Kelly’s work on liberal egalitarianism has concentrated on its claims as a political theory and his most recent work is on the defence of liberal moralism against the arguments of ‘realist’ political theorists such as Bernard Williams.