Little is recorded of his life before 1545. He probably attended St. Andrews Univ., where he may have become acquainted with some of the new Protestant doctrines. He entered the Roman Catholic priesthood, however, and from 1540 to 1544 was engaged as an ecclesiastical notary and as a private tutor.
By late 1545 Knox had attached himself closely to the reformer George Wishart. When, after Wishart's execution (1546), a group of Protestant conspirators took revenge by murdering Cardinal David Beaton, Knox, now definitely a Protestant, took refuge with them in St. Andrews Castle and preached in the parish church. Attacked by both Scottish and French forces, the castle was eventually surrendered (1547), and Knox served 19 months in the French galleys before his release (1549) through the efforts of the English government of Edward VI.
Knox spent the next few years in England, preaching in Berwick and Newcastle as a licensed minister of the crown and serving briefly as a royal chaplain. He helped to prepare the second Book of Common Prayer, but he declined a bishopric in the newly established Church of England.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.