Sir John was appointed a High Court judge in 1992, and in 1999 appointed to the Court of Appeal. He retired in 2016 to take up the one-year post of A. L. Goodhart Visiting Professor of Legal Science at Cambridge University.
Prior to his judicial career, Sir John had a highly successful practice at the Bar. He was called in 1970 and practised from 39 Essex Chambers (formerly 2 Garden Court) throughout his career. He was appointed First Junior Counsel to the Treasury (Common Law) in 1984 and a Recorder in 1985.
Sir John is President of the Constitutional and Administrative Law Bar Association (ALBA); the Bar European Group and the Proceeds of Crime Lawyers Association.