Smyth or Smith, John, c.1554–1612, English nonconformist clergyman and early believer in adult baptism. Influenced by the Brownists, he separated from the Church of England and became (1606) minister of an independent congregation at Gainsborough. Shortly thereafter he and his followers went to Holland to escape persecution. There, under Mennonite influence, he became convinced that the Scriptures did not authorize infant baptism; he baptized himself (for which he was called se-baptist, or self-baptizer) and some of his followers. Later he was excommunicated by his followers. He attempted to join the Mennonite church, was refused admission and died soon after.
See biography in Smyth's works (ed. by W. T. Whitley, 1915); W. H. Burgess, John Smith the Se-Baptist (1911).