He was appointed QC in 1960, Recorder of Grimsby (1961–63) and Recorder of Derby (1963–65). He received considerable public attention in 1963 when he appeared for the prosecution in the Great Train Robbery trial. In 1964, James was asked to chair the statutory inquiry into the circumstances surrounding the Metropolitan Police's Detective Sergeant Harold Challenor's being able to plant evidence and assault suspects. In 1965 he was appointed a High Court Judge, assigned to the Queen's Bench Division. He received the customary knighthood on his appointment. He was elected to an honorary fellowship of Jesus College in 1972. He was promoted to the Court of Appeal in 1973 and was sworn as a member of the Privy Council accordingly. He had a reputation as a hard-working judge. When he was a member of the Court of Appeal, it was once said (albeit with some exaggeration) that James made more decisions on criminal cases than the rest of his fellow judges put together, when taking into account decisions made without open court hearings.