The family's first contact with Methodism was through Marmaduke Gwynne (1692-1769) who entered Jesus College, Oxford, on 5 May 1710 and Lincoln's Inn in 1711, but then abandoned his education and married Sarah Evans of Fynnon Bedr, Cardiganshire, on 27 July 1716. Converted through hearing Howell Harris preach in 1737, he became involved in the revival by giving his support to the leaders and also by intervening on behalf of Methodists when they were threatened with prosecution. He helped Howell Harris in the matter of his marriage to Anne Williams of Skreen in 1744, was present in Bristol in 1745 at Wesley's second Conference, and on 8 April 1749 his daughter, Sarah Gwynne (1726-1822), became the wife of Charles Wesley. (They were married at Llanlleonfel church, a predecessor of the present 19th century building.) After the wedding Gwynne removed to Ludlow; two years later he returned to Wales and resided at Brecon until his death in 1769.
His eldest son, Howell Gwynne (1718-1780), was MP for Radnorshire, 1755-1761, and for Old Sarum, Wiltshire, 1761-1768. By the beginning of the nineteenth century, the family was no longer living at Garth but at Glanbrân near Llandovery, and Llanelwedd near Builth Wells.