German theologian and early supporter of Martin Luther (Luther, Martin) who later dissented from Lutheran views by pressing for more extensive reforms in theology and church life.

Educated at Erfurt and Cologne, Carlstadt was appointed professor at the University of Wittenberg in 1505. There he assisted his colleague Martin Luther in reforming theological studies, emphasizing “the old Fathers,” particularly Augustine (Augustine, Saint), and philology.

Carlstadt supported his colleague Luther during the indulgence controversy, in which Luther opposed the elaborate Roman Catholic system for pardoning sinners and exempting them from purgatorial punishment. Carlstadt defended Luther against Johann Eck (Eck, Johann) in the Leipzig disputation of July 1519. The papal bull issued by Leo X in 1520, threatening Luther with excommunication, also mentioned Carlstadt. In 1521 Carlstadt went to Denmark at the request of King Christian II, but he returned to Germany after his efforts at reform failed. He published numerous tracts on clerical celibacy, private masses, and Holy Communion by both bread and wine, so that by the end of 1521 he had gained a reputation as a forceful Reformer. On Christmas Day in 1521, without vestments and with an abridged service, he administered Holy Communion to the laity.

At Wittenberg in January 1522, the magistrates carried through practical reforms stemming in part from Luther's ideas and Carlstadt's initiative. But, because of his iconoclastic tract Von Abtuhung der Bylder (1522; “On the Rejection of Images”), Carlstadt was called in February by the elector Frederick the Wise (Frederick III) to account for his part in the prevailing ferment. Luther, who during the turmoil had been at Wartburg Castle, came out of hiding to urge restraint. In a series of masterful sermons stressing the need for care of the weaker brethren, Luther disputed Carlstadt's impatience for further reform.

Carlstadt soon fled and began to dress as a peasant, calling himself “Brother Andreas” and denouncing all academic degrees and distinctions. In 1523 he moved to Orlamünde, where he introduced his own program for reform. Influenced by the mystic Johann Tauler (Tauler, Johann), he published a stream of pamphlets full of mystical notions. He dramatically encountered Luther at Jena in August of the next year, when Luther tossed a golden coin at him in token of an open feud. As Luther left, Carlstadt preached against him amid pealing bells.

Carlstadt was promptly expelled from Saxony, but not before he published a series of tracts asserting the belief in the symbolic presence of Christ in the Eucharist. Carlstadt's work Ob man gemach faren soll (1524; “Shall We Go Slowly?”) was eagerly read by all those for whom reform came too slowly. Luther, nevertheless, provided refuge for Carlstadt in Wittenberg (1525–29) after Carlstadt made certain retractions. After short stays in Holstein, Friesland, and Zürich, Carlstadt became professor of Old Testament at Basel in 1534. There he became involved in a controversy by demanding that the local clergy submit to university discipline and earn doctoral degrees in order to improve their credentials. Thus, in supporting the position of the university, Carlstadt reversed his earlier opposition to academic discipline and a learned ministry. A man of theological insights but eccentric personality, Carlstadt persisted in his intense style until his death during an outbreak of the plague.