David joined Fitzwilliam in 1969 as the first Fitzwilliam-based Law Fellow and Director of Studies in Law. He left Fitz 1989 when he became Professor of Law and Dean of the Law School at the University of East Anglia. He has been a Life Fellow of Fitzwilliam since 1989.
In 1994 he left academic life when he was appointed to the Judiciary as a Circuit Judge. Whilst holding judicial office, he held a number of posts including  President of the Immigration Appeals Tribunal, President of the Care Standards Tribunal, A Deputy High Court Judge sitting in the Administrative Court and the Family Division, the Director of Studies of the Judicial Studies Board, and a Commissioner of the Judicial Appointments Commission. 
In 2012, he retired as a Judge and was appointed by the General Medical Council to establish the Medical Practitioners Tribunal Service to hear cases brought by the GMC involving practitioners whose fitness to practice was being assessed.
He retired from that position in 2017. Most recently he wrote a Report commissioned by the Archbishops Council into the handling of allegations that came to the attention of the Church of England concerning a former and now deceased Bishop. This was published in 2021 entitled ‘A Betrayal of Trust’.