Williams was born the son of Samuel Williams, Vicar of Llandyfriog and Rector of Llangynllo, Cardiganshire, and his wife, Margaret, daughter of Jenkin Powell Prytherch, in Y Glaslyn, near Llandysul, Ceredigion, in south-west Wales. He was ordained deacon in 1708 and priest in 1713. He was married to Margaret Davies of Cwmwysg, Defynnog.
Williams later served as Curate of Chiddingstone, Kent (1708–1713), Vicar of Llanwenog, Cardiganshire (1715–1742), Vicar of Defynnog (Devynock), Brecknockshire, where his name is carved on one of the attic beams of the rectory (1716–1732), Rector of Chilton Trinity, Somerset, and finally Vicar of St Mary's, Bridgwater (1732–1742).
Williams supervised new editions of the Bible and Book of Common Prayer in Welsh. His library, containing many Welsh books and manuscripts, came into the possession of William Jones and then into the library of George Parker, 2nd Earl of Macclesfield at Shirburn Castle.