Professor Clarke has been a senior Specialist Advisor to the House of Commons Defence Committee since 1997, having served previously with the House of Commons Foreign Affairs Committee. In 2004 he was appointed the UK member of the United Nations Secretary General's Advisory Board on Disarmament Matters. He has published extensively on defence and security issues and has lectured at many universities in the United Kingdom, as well as at the Joint Staff College, the Royal College of Defence Studies, the NATO School at Oberammergau and the Clingendael Institute in the Netherlands. He has been a Guest Fellow at the Brookings Institution in Washington and a Fellow in British Foreign Policy at the Royal Institute of International Affairs, of whose Council he has been a member since 2004.