He was Research Associate in the Department of Physics, Princeton University (1975-1976) and a Junior Lecturer, University of Oxford (1976-1977). In 1977, he was made a Fellow of Wadham College, University of Oxford, where he has been an Emeritus Fellow since 1988. He was Head of the
Mathematical Institute, University of Oxford (2001-2009). He served as Treasurer of the
London Mathematical Society (2002-2009) and President of the Clay Mathematics Institute (2012-2018). His research is in applications of geometry in mathematical physics. == Honours ==