Stephen is a senior historian at The National Archives. He obtained his PhD from the Centre of Science, Technology and Medicine at the University of Manchester and was a Post-Doctoral Research Fellow at the Department of International Politics, University of Wales, Aberystwyth.

During his time at The National Archives, Stephen completed a four-year secondment at the Foreign and Commonwealth Office where he was responsible for editing three volumes of documents on British Policy Overseas, the official record of British foreign policy.

Stephen is a fellow of the Royal Historical Society and a member of the Arts and Humanities Research Council's Peer Review College. He has published a number of books and articles on the Cold War and has made regular media appearances to discuss record releases at The National Archives.