Edwards began preaching when about 22, having come under the influence of Edmund Jones (q.v.) and that of Harri Smith, his labourer at Bryn-tail, whose eloquence had astonished that ‘Old Prophet.’ In 1743 a small meeting-house was built beside a field named Waen-fach, near the site of the present Independent chapel at Groes-wen. The congregation, originally a Methodist society, incorporated itself as an Independent church in 1745 and ordained Edwards and Thomas William (1717-1765) (q.v.) as its joint pastors. The latter d. twenty years later; Edwards remained sole pastor until his death. He is, however, best remembered as a builder of bridges, or more precisely, as the architect of Pontypridd bridge, one of the most dangerous and least serviceable of large bridges in Wales, so much so that the nearby ford was still used until the middle of the 19th cent. The appeal of the bridge was indeed purely aesthetic and scientific. Its unique design, rare beauty, and technical secrets, have made it the most controversial bridge in Britain, and brought its designer lasting fame. He had constructed industrial buildings before he contracted, in 1746, to build a bridge at Pont-y-tŷ-pridd, a tiny hamlet, so named long before Edwards was born and therefore before its famous bridge became associated with it. Nothing is known of the original ‘Pont-y-tŷ-pridd.’ For the history of Edwards's endeavours at Pontypridd, we are chiefly indebted to his friend and former neighbour, Thomas Morgan (1720-1799) (q.v.). Morgan's account was amplified and slightly corrected by the architect himself. Edwards made four attempts (1746-54) before he succeeded in completing his contract to build, for £500, a bridge that would stand for seven years. Finally, he lessened the pressure on the haunches of the arch by providing three cylindrical holes in each of them and by varying the thickness of the parapets. These bridges cost, in all, £1,153 18s. 2d. This, with attendant expenses, resulted in a loss to the builder of about £600. He erected bridges also at Usk, Pontardawe, Betws (Glam.), Dolau-hirion, Wychtree, Aberavon, and Glasbury. Some of these were single-arched, and less steep than Pontypridd bridge. He did much bridge work in Monmouthshire, and contracted to rebuild Chepstow bridge, but did not do so. So numerous were the demands for Edwards's engineering services, that building and repairing bridges became the occupation of three of his sons — THOMAS, DAVID, and EDWARD. The fourth, WILLIAM, was killed at Gibraltar, a war victim. The first two built Newport bridge, finished in 1801. Among others constructed by them were Llandilo, Edwinsford, and Bedwas.

William Edwards wrote but little. Six of his hymns were published in 1747.