He was the son of John Stewart, the Younger, of Traquair in Peeblesshire, of a branch, originally illegitimate, of the house of Buchan.

He was, however, compelled to publish Charles's proclamation enforcing the use of the liturgy and forbidding hostile demonstrations on pain of treason (1638).

[5] After the Treaty of Berwick he was appointed the king's commissioner to the assembly at Edinburgh (August 1639), and he assented in writing to the act abolishing episcopacy, but prevented its ratification by adjourning the opening of parliament.

In his absence he was sentenced to death, but, although the king secured the remission of this penalty, he was dismissed from his office of treasurer, and in 1644, for repairing to the court and opposing the covenant, he was declared an enemy to religion and fined 40,000 marks.

He was succeeded by his only son John (c. 1622–1666), whose descendants held the title until 1861, when on the death of Charles, the 8th earl, it became dormant or extinct.