John Calvin moved from legal and humanist studies into Protestant reform during the early 1530s. His first edition of the Institutes of the Christian Religion appeared at Basel in 1536, presenting a systematic defense and explanation of reforming Christian beliefs. Traveling through Geneva that year, he was persuaded by William Farel to remain and help organize the church. Conflict over discipline and relations with the city authorities led to their expulsion in 1538.

Calvin spent the next three years in Strasbourg, ministering to a French-speaking refugee congregation and learning from Martin Bucer's approach to church organization. He revised the Institutes, wrote biblical commentary, and participated in theological negotiations. Recalled to Geneva in 1541, he helped establish ecclesiastical ordinances assigning responsibilities to pastors, teachers, elders, and deacons. The Consistory supervised religious and moral conduct, although its authority and relationship with the civil councils remained contested rather than simply controlled by Calvin alone.

His work combined frequent preaching, lectures, correspondence, and extensive commentaries on scripture. Successive editions of the Institutes culminated in the expanded Latin edition of 1559. He emphasized the sovereignty of God, justification by faith, the disciplined life of the church, and the role of scripture. Predestination became a prominent element of later Calvinist identity, but it was one part of a larger theological program.

Calvin supported the prosecution of Michael Servetus for heresy in Geneva in 1553. The city authorities ordered Servetus burned; Calvin opposed his teachings and defended the punishment, though he preferred another method of execution. This episode exposes the coercive limits of his reform and cannot be omitted from an account of his influence. The Genevan Academy, founded in 1559, trained ministers and teachers who carried Reformed Protestantism into France, Scotland, the Netherlands, and elsewhere. Refugees and correspondence networks also spread his ideas. Calvin died in 1564. His career created durable patterns of theology, worship, education, and church discipline, but the subsequent traditions called Calvinist developed through many followers and differed across political settings. His effectiveness as an organizer and writer existed alongside intolerance toward dissent and persistent struggles over who could govern religious and civic life.