John Tudno Williams (born 31 December 1938) was the Moderator of the Presbyterian Church of Wales 2006–7 and the Principal of the United Theological College, Aberystwyth from 1998 to 2003.
John Tudno Williams was born in 1938 in Flint, the son of Arthur Tudno Williams, a minister in the Presbyterian Church of Wales and an alumnus of Jesus College, Oxford, and Primrose (née Hughes Parry). He was educated at the Liverpool Institute High School for Boys in Liverpool and Colfe's Grammar School in London. Williams studied theology at Jesus College, Oxford like his father before him, graduating in 1960. On leaving Oxford, he registered as a research student in the Classics Department of University College of Wales, Aberystwyth, whilst studying at the same time at the United Theological College, Aberystwyth, in preparation for ministry in the Presbyterian Church of Wales. He was ordained in 1963 and served at Borth, in north Cardiganshire, for ten years. In 1976 he gained a doctorate from the University of Wales for a research thesis on the Jewish background to St John's Gospel.
In 1966 Williams joined the teaching staff at the United Theological College, Aberystwyth, under its principal, the Revd Samuel Ifor Enoch, lecturing in Biblical studies. Williams took leading baritone roles in the University College's Gilbert and Sullivan Society, then under the conductor David Russell Hulme.