John studied for his PhD at the University of Warwick (1992-96), working on legitimacy in international relations and the collapse of Yugoslavia, following which he became a Lecturer at the University of Aberdeen for five years before joining Durham in 2001. John was promoted to Senior Lecturer in 2006 and to Professor in 2010.

John's research in recent years has revolved around three, interconnected issues. First is the English school of international relations theory, where he has worked on both analysis of classic texts and also on the development of ethical dimensions of the School's approach. Second, is the wider area of international political theory, where he has concentrated on ethical dimensions of issues such as territory, space and political violence. This has also brought his research into contact with related debates in political geography. Thirdly is the area of the Just War tradition, where his work has looked at the challenges to standard accounts of the ethics of war presented by changing patterns and technologies of violence and the issue of democratic authority over warfare.

John has just completed a book-length study of diversity and ethics in English school theory, seeking to develop an alternative to the 'pluralist' position as it is usually presented. This is now published by Oxford University Press as 'Ethics, Diversity and World Politics: Saving Pluralism From Itself?' .

John is also working on a project looking at the ethics of automatic and autonomous weapons and security systems. The first output of this work - 'Distant Intimcay: Space, Drones and Just War' - was published in the spring 2015 edition of Ethics & International Affairs. A second paper on regulating autonomous weapons was published in Global Policy in Spetember 2015.