Martin Luther's public career began in the university and church, where his study of scripture developed into a challenge to papal authority. An Augustinian friar, he became a doctor of theology and professor at Wittenberg in 1512. His lectures and religious concerns led him to emphasize justification through faith and divine grace. In 1517 he circulated the Ninety-five Theses against abuses associated with indulgences. The conventional story of their posting on a church door is debated, but their publication and rapid spread made the dispute a public controversy.

Debates and investigations broadened the conflict beyond indulgences. In major writings of 1520, Luther challenged the church's sacramental system, urged reform through secular authorities, and described Christian freedom. Pope Leo X condemned his teachings, and Luther burned the papal bull. Excommunicated in 1521, he refused to retract at the Diet of Worms unless convinced by scripture and reasoned argument. The imperial edict declared him an outlaw. Frederick the Wise's protection allowed him to live secretly at the Wartburg, where he translated the New Testament into German; it appeared in print in 1522.

Returning to Wittenberg, Luther sought to guide reform while opposing changes he considered disorderly or theologically mistaken. He worked with colleagues, including Philipp Melanchthon, on teaching, worship, church organization, and translation. He married Katharina von Bora in 1525. His catechisms, hymns, and sermons brought the movement into households and congregations, while the complete German Bible published in 1534 helped shape religious reading and written language. These achievements depended on collaborators and printers as well as Luther's own authorship.

His movement also generated conflicts with other reformers, particularly over the Eucharist, and relied increasingly on the protection and authority of territorial rulers. During the Peasants' War he urged violent suppression of rebellion, revealing limits to the freedom he envisaged. His late writings against Jews, including On the Jews and Their Lies in 1543, advocated destructive persecution; they remain a grave part of his record and later antisemitic reception. Luther died in Eisleben in 1546 after continued preaching, writing, and mediation. His career helped transform western Christianity by making scripture, vernacular teaching, and a changed understanding of salvation central to institutional reform.