Like his father he was one of the most influential members of the party of religious reform, signing what was probably the first "godly band" in December 1557, and Argyll soon became one of the leaders of the Lords of the Congregation.
Mary wore a "marvellous fair" costume which had been a gift from Agnes Campbell the wife of James MacConel or MacDonald of Dunyvaig.
It was said that Argyll was a leader of a plot to kidnap Mary and Henry Stuart, Lord Darnley in June 1565 as they travelled between Perth and Edinburgh.
[9] When the English failed to help their Scottish allies, Argyll, alone of the rebels, was able to remain in the Kingdom, due to his very strong position in the Highlands.
Although supposed to be a signatory of the Ainslie Tavern Bond,[11] Argyll was horrified by the Queen's marriage to James Hepburn, 4th Earl of Bothwell.
He continued to champion the queen's cause following her flight to England, but eventually reconciled with the regent Lennox in 1571, and lent his support to the King's party, as a means of restoring peace and lessening English meddling in Scottish affairs.
[13] He first married Lady Jean Stewart (died 1588), daughter of James V of Scotland and Elizabeth Bethune; he was thus half-brother-in-law to Mary and to Moray.