He was called to the bar at Gray's Inn in 1956 before moving to One Hare Court alongside Henry Fisher, Patrick Neill, Roger Parker, and Richard Southwell, becoming a bencher in 1970 and Treasurer in 1988.

He was appointed Recorder of Hereford in 1971 and as a judge of the Queen's Bench Division of the High Court in 1976, receiving the customary knighthood,[2] serving additionally as President of the Employment Appeal Tribunal from 1978.

He was appointed a Lord of Appeal in Ordinary on 11 March 1992, becoming a life peer as Baron Slynn of Hadley, of Eggington in the County of Bedfordshire,[3] and being sworn of the Privy Council.

He was a Trustee of The Loomba Trust, which cares for widows around the world, and Patron of the Bharatiya Vidya Bhavan Institute for Indian art and culture.

He was appointed Knight Grand Cross of the Order of the British Empire (GBE) in the 2009 New Year Honours for his services to the International Law Association which he served as Chairman of the Executive Committee.

[9] In 2000 he was presented with a 2-volume Liber Amicorum: Vol I, entitled Judicial Review in European Union Law, was edited by Professor David O'Keeffe and Antonio Bavasso; Vol 2, entitled Judicial Review in International Perspective, was edited by Mads Andenas and Duncan Fairgrieve; both volumes were published by Kluwer Law International (ISBN 90-411 1373-8 (set)).