Born about 1510, he was only sixteen when, circa 26 November 1526, he married Joan Hamilton, illegitimate daughter of the 1st Earl of Arran. As Lord Kilmaurs, he was, like his father, a supporter of 
the Reformed faith as early as 1540. In May 1544, with his father and the Earl of Lennox, he made an agreement with Henry VIII, King of England, which resulted in all three receiving substantial pensions 
from the English king. 
Shortly afterwards they were defeated by Regent Arran at the Battle of Glasgow, where Alexander's younger brother, Andrew, was killed. In September 1544 Alexander and his father declined to assist 
Lennox in his expedition to the west of Scotland. In 1545 he divorced his wife and married Janet Cunningham. 
In 1547 his father died and Alexander became Earl of Glencairn as well as one of the most fervent supporters of John Knox. He was one of the few nobles motivated purely by religious zeal. In 1555, after Knox's return to Scotland, Glencairn invited him to his house at Finlayston near Glasgow, where Knox preached and celebrated the Lord's supper. In March 1557 Glencairn's name appears as first of the four signatories on the letter sent to Knox, inviting him to return from Geneva. His signature also appears second, after the fourth Earl of Argyll, of the five on the first bond of the Scottish Reformers 
subscribed on 3 December 1557. In May 1559 when Marie de Guise, outraged by the destruction of the monasteries by the 'rascal multitude', attempted to march on Perth, Glencairn barred her way with 
2,500 men. 
After the parliament of August 1560, Glencairn, Morton and Maitland of Lethington were sent as ambassadors to Queen Elizabeth to request her assistance against the French invaders and propose a 
marriage between her and the 3rd Earl of Arran. They obtained a favourable reply as the former was concerned, but the latter was flatteringly declined. 
In June 1561, Glencairn, Arran and the 5th Earl of Argyll were commissioned to carry out the edicts of the lords for the destruction of 'all places and monuments of idolatry' in the west. This resulted 
in the ruthless demolition of, among others, the abbeys of Paisley, Fulford, Kilwinning and Crossraguel. 
At the end of 1561, on the return of Mary, Queen of Scots, Glencairn was appointed Privy Councillor but was always intolerant of the queen's papal practices. In June 1565, with other Reformers, he 
vigorously opposed the Darnley marriage and joined Moray on the  'Chaseabout Raid'. In December he was declared guilty of the crime of lese majesty and then went to Berwick but was back in Scotland early the following year. 
He was in Edinburgh at the time of the Rizzio conspiracy but was not involved, and was one of the first of the lords to join Mary at Dunbar after the murder. Thereafter Glencairn became one of the 
queen's chief opponents. He had nothing to do with Darnley's murder, was not in Edinburgh on the night of the signing of the 'Ainslie Bond', and strongly disapproved of the Bothwell marriage. On 15 June 1567 at Carberry, he was one of the leaders of the army under Morton against the queen and Bothwell. A few days later, in an act of futile vandalism, he and his servants demolished the altar, ornaments and images of the Chapel Royal at Holyrood. On 29 July, after Mary's abdication, he carried the sword at the coronation of the infant king. 
In May 1568 Glencairn commanded one of the divisions against Mary at Langside. In September 1571 he was taken prisoner at Stirling on the night that Regent Lennox was killed, but was rescued soon 
afterwards. He frequently visited John Knox on his deathbed and on 24 November, the day of Knox's death, was nominated along with Morton as a candidate for regent but was substantially outvoted. Glencairn died on 23 November 1574.
 

Source: Leo van de Pas