He was created Earl of Loudoun, lord Farrinyeane and Mauchline by patent dated at Theobalds on 12 May 1633, but in consequence of his joining with the George Leslie, Earl of Rothes and others in parliament in their opposition to the court with regard to the act for empowering King Charles I to prescribe the apparel of churchmen,[3] the patent was by a special order stopped at the chancery, and the title superseded.

Soon after the passing of this act, the Scottish bishops resumed their episcopal costume, and in 1636 the Book of Canons Ecclesiastical and the order for using the new service-book were issued upon the sole authority of the King without consulting the general assembly.

By his opposition to the policy of the court, Loudoun became a favourite of the adherents of the popular cause; and on 21 December 1637, at the meeting of the Privy Council at Dalkeith, in an eloquent speech, he detailed the grievances of the "Supplicants", and presented a petition on their behalf.

In these proceedings Loudoun took a very prominent part, and being elected elder for the Burgh of Irvine in the general assembly, which met at Glasgow in November 1638, he was appointed one of the assessors to the Moderator.

No answer was given to the remonstrance, but a few days after Loudoun was committed to the Tower of London upon acknowledging that a letter produced by the Earl of Traquair was in his own handwriting.

According to Dr. Birch, a warrant was made out for Loudoun's execution without trial, but this has not been sufficiently corroborated, and after some months' confinement in the Tower he was liberated upon the intercession of James, Marquis of Hamilton, and returned to Scotland.

[5] In August 1641 the King opened the Parliament of Scotland in person, the treaty with England was ratified, and offices and titles of honour were conferred on the "prime covenanters who were thought most capable to do him service".

[5] Accordingly, "the principal manager of the rebellion", as Clarendon calls him, was appointed Lord Chancellor of Scotland on 30 September 1641, and on 2 October took the oath of office, and received from the King the Great Seal, which, since the resignation of John Spottiswoode, the Archbishop of St. Andrews, had been kept by the Marquis of Hamilton.

Charles, however, would not admit that the act of pacification gave the Scottish council any authority to mediate, and refused to allow the commissioners to proceed to London for that purpose.

Persuaded by the more violent party of the Covenanters, who denounced the "Engagement" as "an unlawful confederacy with the enemies of God",[5] he changed sides and opposed the measure.

[5] After the Battle of Worcester (September 1651) Loudoun retired into the highlands, and in 1653 joined William, Earl of Glencairn and other Cavaliers who had risen in the King's favour.

Upon the Restoration, notwithstanding all that Loudoun had suffered for the royal cause, he was deprived of the chancellorship, which had been granted to him "ad vitam aut culpam"; his pension, however, was still continued to him.

[5] In the first session of parliament in 1661 he spoke strongly in defence of his friend, the Archibald Campbell, Marquess of Argyll, who was then under an impeachment for high treason.