English separatist; b., probably at Swanton, near Norwich, 1571; d. at Amsterdam 1622 or 1623. Driven from England, about 1593 he went to Amsterdam, and in two or three years became "teacher" of the congregation of which Francis Johnson (q.v.) was minister. He and Johnson could not agree and the congregation divided in 1610. In 1612 Johnson went to Emden, and thenceforth Ainsworth had the field to himself. It has been inferred that he lacked a university training from a statement of Roger Williams, that "he scarce set foot within a college walls" (Bloody Tenet, 1644, p. 174; cf. Dexter, 270, note 68); but the register of Caius College, Cambridge, shows that he was admitted there Dec.15, 1587, and was in residence there as a scholar for four years. He was unquestionably a learned man, wrote excellent Latin, and had a knowledge of Hebrew (perfected by association with Amsterdam Jews), equaled by that of few other Christians of his time. He was earnest and sincere in his faith, conciliatory in spirit, and moderate in controversy. He had the chief part in drafting the Congregational Confession of 1596 (entitled A True Confession of the Faith, and Humble Acknowledgment of the Allegiance which we, her Majesty's subjects, falsely called Brownists, do hold towards God, and yield to her Majesty and all other that are over us in the Lord; cf. Walker, pp.41-74, where the full text is given). He wrote many controversial works (for full list consult DNB, i. 192-193) and a series of Annotations upon the books of the Pentateuch, the Psalms, and the Song of Songs (1612 sqq.; collected ed., London, 1626-27; reprinted, 2 vols., Glasgow, 1843), which have still some value.

Bibliography: H. M. Dexter, Congregationalism of the Last Three Hundred Years, New York, 1890; W. Walker, Creeds and Platforms of Congregationalism, p. 43, note 1, New York, 1893.