He was the son of
John Erskine, Earl of Mar (1558–1634) and Anne Drummond (1555-1587), daughter of Lord David Drummond (d. 1571) and
Lilias Ruthven. Until his father's death in 1634, he was known as John, Lord Erskine, or the "Master of Mar".
Prince Henry, the son of
James VI and I and
Anne of Denmark was kept at
Stirling Castle. After the
Union of the Crowns in 1603, King James went to England. Anne of Denmark came to Stirling on 10 May to claim her son. The Earl of Mar was absent. John Erskine and his step-mother
Marie Stewart, Countess of Mar denied the queen's request to take Henry away. His father arrived on 12 May and sent him to London with messages for the king. According to the Earl of Mar, King James forgave his family for this, thinking that his "young son and honest poor friends have done nothing but served him faithfully". John Erskine and other Scottish courtiers were admitted as members of
Gray's Inn on 22 May 1603. John Erskine went to Venice in May 1605 and the ambassador
Henry Wotton introduced him to the
Doge,
Marino Grimani, who complimented him on his noble good looks. Erskine took part in the masque at the wedding of
John Ramsay, Viscount Haddington and Elizabeth Radclyffe, daughter of
Robert Radclyffe, 5th Earl of Sussex in February 1608 known as ''Lord Haddington's Masque
or The Hue and Cry After Cupid''. Erskine was knighted on 30 May 1610 at the creation of Prince Henry as
Prince of Wales. A detailed bill for Lord Erskine's clothes from an English tailor survives from May 1611. In 1612 Erskine unsuccessfully advocated for a knighthood to be given to the laird of
Findlater. In September 1613 Erskine hosted the Venetian ambassador
Antonio Foscarini at
Stirling Castle. Foscarini had travelled to Scotland after discussing the country with
Anne of Denmark. Repairs to
Edinburgh Castle and
Holyrood Palace in 1624 made by a carpenter Arthur Hamilton include work in "Lady Erskyne's studie" and "Lady Marre's gallery". A blacksmith Thomas Brown made new fittings for Lord Erskine's hall door in the castle. On 29 December 1634, John Erskine wrote from
Edinburgh Castle to
Charles I with news of his father's death. In 1638 he wrote to king about the poor state of repair of
Stirling Castle and the walls of the park, and the
Earl of Traquair was ordered to make repairs. In 1645 Robert
Farquharson of
Invercauld was the keeper of
Kildrummy Castle for the earl and his son Lord Erskine. The laird of
Glenkindie also helped to keep the castle, fearing the depredations that a garrison of "stranger" soldiers would make on his lands. The main residence of the Earl of Mar was
Alloa Tower. ==Marriage and children==