Elwyn Jones was born in Llanelli, Carmarthenshire, and read history for a year at the University of Wales, Aberystwyth, and then at Gonville and Caius College, Cambridge.

In 1964, Elwyn Jones was sworn of the Privy Council and appointed Attorney General (receiving the customary knighthood[5]) by Harold Wilson, a post he held until 1970.

In February 1974, he was once again elected to Parliament, now for Newham South, but left the House of Commons soon afterwards when he was made a life peer.

[1] The resulting by-election allowed Nigel Spearing to re-enter Parliament as he had lost the Acton seat in the February election.

Elwyn-Jones's brother Idris (1900–1971) was captain of the Wales rugby union team in 1925, and was an industrial chemist who became Director General of Research Development for the National Coal Board.