The Reformation in Sweden is generally regarded as having begun in 1527 during the reign of King Gustav I of Sweden, but the process was slow and was not definitively decided until the Uppsala Synod of 1593, in the wake of an attempted counter-reformation during the reign of John III (1568–1592).

Gustav I, commonly known as Gustav Vasa, was King of Sweden from 1523 until his death in 1560, previously self-recognised Protector of the Realm (Riksföreståndare) from 1521, during the ongoing Swedish War of Liberation against King Christian II of Denmark, Norway and Sweden. Gustav rose to lead the Swedish War of Liberation following the Stockholm Bloodbath, where his father was executed. Gustav's election as king on 6 June 1523 and his triumphant entry into Stockholm eleven days later marked Sweden's final secession from the Kalmar Union.