A poet and author, he wrote hymns in both English and Welsh. Sometimes critical of his mentor, Howell Harris, Williams nevertheless devoted himself to the movement, travelling throughout Wales to preach and convert. His hymns alone made a major contribution to the success of Calvinistic Methodism. His best-known works include the long poem, "Bywyd a Marwolaeth Theomemphus" (1764), and hymns such as "Now the shadows flee and vanish". His virtuosity earned him another nickname: Y Per Ganiedydd ("The Sweet Singer").