He was converted in 1741 during a visit by Charles Wesley to his home at Llanishen near Cardiff and soon afterwards became one of John Wesley's itinerant preachers. Having been involved in the conflicts with Anglican clergy in Darlaston and Walsall in 1743, he was criticized by John Wesley for his 'inexcusable folly' at Wednesbury. This led to an estrangement between him and the Wesleys, whom he is said to have deemed 'Papists, tyrants, enemies of the Church'. In 1744 his bid for episcopal ordination was foiled by Charles Wesley and his resentment may account for his persistently accepting and publicizing scandalous rumours about Wesley's alleged immoral conduct. For this he was expelled from the itinerancy by John Wesley in August 1744, but by the end of the year he had recanted and been reinstated, though only as a probationer. In March 1746 he went, probably at Wesley's request, to Dublin, where a small society had grown under the leadership of John Cennick into a flourishing Moravian-type society. Arriving in August 1747 Wesley found there a Methodist society of some 280 members, the result of Williams' powerful preaching and enthusiastic leadership. This led A.H. Williams to claim for him such titles as 'father' and 'pioneer' of Irish Methodism, though significantly another preacher was put in charge of the work. From 1749 on he was back in the English work, until finally expelled in 1755 for an unknown offence. He was later ordained into the Anglican ministry through the good offices of Lady Huntingdon.