Knox first appears in public records as a priest and a notary in 1540. He was still serving in these capacities as late as 1543 when he described himself as a "minister of the sacred altar in the diocese of St. Andrews, notary by apostolic authority" in a notarial deed dated 27 March. Rather than taking up parochial duties in a parish, he became tutor to two sons of Hugh Douglas of Longniddry. He also taught the son of John Cockburn of Ormiston. Both of these lairds had embraced the new religious ideas of the Reformation.