Paul trained in psychiatry at the Maudsley Hospital and at the Institute of Psychiatry.
For nearly 20 years he worked in the Medical Research Council Social Psychiatry Unit at the Institute of Psychiatry, initially under John Wing, and eventually becoming Assistant Director. In 1996, he moved to University College London (UCL) to a Chair in Social & Community Psychiatry. At the same time, he also took up an honorary consultant post with the Camden & Islington National Health Service Trust, working in a series of clinical appointments. The last of these was with the Community Mental Health Inreach Team in Holloway women’s prison, over the six years until September 2010. He was Head of the Department of Mental Health Sciences at UCL from 2004 until November 2009. He became Professor Emeritus at UCL in October 2010 on his retirement.
Paul has published widely on epidemiological issues, on mental health services, and on psychological theories and treatments of psychosis. With colleagues he has conducted a number of randomized controlled trials of psychiatric interventions and psychological treatments. He recently carried out a large study of psychiatric treatment needs in two prisons. He has been involved in the organization and design of all three British National Surveys of Psychiatric Morbidity. He was the founding editor of the International Review of Psychiatry, and has been the Editor-in-Chief of Social Psychiatry and Psychiatric Epidemiology since 1993.