After studies at Freiburg im Breisgau, Haetzer was probably consecrated as a priest and given a chaplaincy near Zürich. He abandoned his position by 1523 and went to Zürich, where he joined the Reformation and became a literary polemicist in its support. His condemnation of the use of images in Judicium Dei (1523; “The Judgment of God”) proved influential in the Reformers’ efforts to combat images in the churches. He wrote Ein Beweis (1524; “One Proof”), a work on the conversion of the Jews, and other works of theology and polemic. He also produced many translations of the works of other Reformers and wrote numerous hymns that are important in the Anabaptist tradition.
In early 1525 Haetzer was expelled from Zürich for his ties to the Swiss Brethren, the incipient Anabaptist movement. He moved to Augsburg but was again expelled and went to Basel, where he was favourably received by the Swiss Reformer John Oecolampadius. After a brief visit to Zürich, where he provoked the opposition of Huldrych Zwingli, Haetzer moved to Strasbourg. There in 1526 he met the Anabaptist Hans Denck, who collaborated with him in the production of his major work, a translation of the Hebrew Prophets (1527) that preceded Martin Luther’s translation by five years. In 1528 Haetzer was arrested and imprisoned in Constance on a charge of adultery, though his opposition to the Trinitarian concept of God was more likely the true cause. He was sentenced to death and beheaded on the very spot where Jan Hus had been burned a century before.