He had been educated for the church but, after the death of his two brothers, became heir unexpectedly. After the death of his father, Edinburgh Castle came into the hands of the Duke of Chatellerault who, in 1554, relinquished it when Marie de Guise became regent. Then the
parliament gave John Erskine custody of the castle with the proviso that he should prevent it from falling into the hands of the French.

At this stage John Erskine had not become a supporter of the Reformed doctrines, although he did so later. Before 29 January 1557 he married Annabella Murray and they became the parents of a son and a
daughter. In 1557, with Lord Lorne, later 5th Earl of Argyll, and Lord James Stewart, later Earl of Moray, and also the Earl of Glencairn, he invited John Knox to return from Geneva.

In 1559 he supported Marie de Guise in her vain effort to prevent the surrender of Perth. His chief motive was to prevent the miseries of civil war. Although his sympathies were by now entirely
with the Reformers, he remained courteous to Marie de Guise, even receive her into Edinburgh Castle in the interest of peace.

In 1561, on the return of Mary, Queen of Scots, John Erskine was appointed a member of the Privy Council, and received a grant of several church lands. He favoured the proposal for the marriage of
Queen Mary to Leicester but, on discovering her feelings, cordially supported the Darnley match.

On 23 June 1565 John Erskine was created Earl of Mar. He was present at the marriage of Mary and Darnley, and thereafter assisted Mary in the Chaseabout Raid. Mar had nothing to do with the murders of either Rizzio or Darnley but, while lying ill at Stirling, shortly before the trial of Bothwell, consented that Edinburgh Castle should be delivered up to Bothwell at the instance of Mary.

On 19 April 1567 he was confirmed in his captainship of Stirling Castle, so that he should be entrusted with the guardianship of the young prince there. He was not even asked to be a signatory to the
Ainslie Bond and later refused to deliver up the young prince to Bothwell.

On 14 June 1567 at Carberry, he was present at the surrender of the queen and two days later signed the order for her commitment at Lochleven Castle. On the 24th he was one of the council to whom she
demitted the government and, on the 29th, he carried the young prince in his arms to his coronation.

On Mary's escape from Lochleven, he sent a supply of men to Regent Moray from Stirling and, on 13 May 1568, was present at the battle of Langside. After Moray's murder, he was one of those who bore
the regent's body at the funeral. On 3 September 1571, the king's party was surprised by the Hamiltons and others near Stirling. Mar gallantly opened fire on the intruders and drove them off, but not before Regent Lennox was killed. Mar was then by general consent chosen regent.

On 10 September, he came to Leith where he proclaimed Morton lieutenant-general of the forces, and from then on until his death, he was effectively Morton's pawn, albeit occasionally unwillingly. The
remainder of his short regency was undistinguished, being notable only for his efforts to secure the surrender of Edinburgh Castle which was still being held for the queen.

On 9 October 1572, a conference took place between Morton, Mar and Killigrew when the proposal was mooted on behalf of Queen Elizabeth that Mary, Queen of Scots, should be delivered up to her
enemies in Scotland with a view to her execution, but Mar did not express much enthusiasm for this plan. Shortly after this conference, Mar was seized with a violent sickness from which he died on 29
October 1572.
 

Source: Leo van de Pas