 Glencairn was amongst the nobles who opposed the marriage of Mary, Queen of Scots, with Lord Darnley.Glencairn later had a principal command in the army embodied against the Queen in June 1567 at the 'battle' of Carberry Hill, and when the French ambassador came from the Queen, promising the forgiveness if they would disperse, he replied that "they came not to ask pardon for any offence they had done, but to grant pardon to those who had offended".When Mary, Queen of Scots, was taken to Loch Leven Castle that month, Glencairn hastened with his domestics to the Chapel Royal of Holyroodhouse and destroyed all the sacred images, demolished the altar, tore down the pictures, and defaced all the ornaments.