Scottish conspirator during the Reformation.

An early adherent of the Reformation, he was during his public life frequently in the pay and service of England, although he fought on the Scottish side at the Battle of Solway Moss (1542), where he was taken prisoner. Upon his release early in 1543 he promised to adhere to Henry VIII, who was anxious to bring Scotland under his rule, and in 1544 he entered into other engagements with Henry, undertaking inter alia to deliver Mary, Queen of Scots, to the English King. However, he was defeated by James Hamilton, earl of Arran, and the project failed; Glencairn then deserted his fellow conspirator, Matthew Stewart, earl of Lennox, and came to terms with the queen-mother, Mary of Guise, and her party.