[3] In religion he was among the leaders of the 18th-century Welsh Methodist revival, along with the evangelists Howell Harris and Daniel Rowland.

He had intended to study medicine, but this changed in 1737–1738, when he was converted by the preaching of the evangelical Methodist revivalist Howell Harris in Talgarth.

Around this time he became involved in the Methodist movement and in June 1742 his disapproving parishioners reported his activities to the Archdeacon's Court in Brecon.

It was nevertheless seen as a threat to the Anglican establishment, and in 1743, when Williams duly applied for ordination as a priest, his application was refused because of his Methodist connection.

Rather than a comfortable, conformist career in the Anglican Church, he chose a financially precarious, but perhaps spiritually richer life as a Methodist preacher.

The key years in the foundation of English Methodism were between 1739, when the brothers Charles and John Wesley, both Anglican priests, broke with the Moravian church and set up their own first chapel in Bristol, and 1743, when they drew up their General Rules.

This was, unfortunately, the very time that Williams was beginning his own career in the Church and partly explains the hostility he experienced from his congregation and from the hierarchy.

Had he lived a little longer, Williams Pantycelyn would no doubt have approved of these moves, because as a Methodist, he himself became a firm advocate of Calvinist Reformation doctrine and frequently invoked stern warnings against Arminianism, Arianism, Socinianism, Sandemanianism and other teachings.

Williams Pantycelyn travelled throughout Wales (he is said to have partly supported his ministry by selling tea)[4] preaching the doctrine of Calvinistic Methodism.

By the same token, it must have been deeply rewarding to see the community grow and thrive over the years and to reflect on the alternative life he had forsaken, as the priest of some obscure rural Anglican parish in mid-Wales.

He wrote two long poems on theological and religious themes: He also wrote a series of elegies in memory of various Methodist and other Christian leaders, including: Griffith Jones of Llanddowror, Howel Davies (the Pembrokeshire preacher), George Whitefield, and Daniel Rowland.