 In May of that year, when the Reformers at Perth found it necessary to protect themselves by force of arms, Glencairn joined them with 1,200 horse and 1,300 foot, which he had raised in the west of the country.After the Protestant religion had been established by parliament in 1560, the earl was nominated a member of Queen Mary's Privy Council.He and the Earl of Morton with William Maitland of Lethington were sent as ambassadors to Queen Elizabeth I of England with a proposal, for the strengthening of the bonds of amity between the two nations, that she should accept as a husband the Earl of Arran, the heir to the Scottish Crown, which she declined.