1702 appointed high commissioner to the general assembly of the church of Scotland. Its proceedings were interrupted by the death of the king, and although Marchmont was immediately appointed commissioner by Queen Anne, the assembly was dissolved before the warrant arrived.
In the first session of the Scottish parliament after Queen Anne's accession, Marchmont, according to Lockhart, `from a headstrong, overgrown zeal, against the advice of his friends and even the commands of my lord `commissioner' (Lockhart Papers, i. 48), presented an act for the abjuration of the Pretender, James, son of James II. Lockhart states that the abjuration was 'in the most horrid scurrilous terms imaginable.' The most violent expression employed was that in which the Pretender was stated not to have `any right or title whatsoever to the crown of Scotland,' thus implying that he was not really the son of James II. After the bill had been read a first time the commissioner, who had made various efforts to bring about a compromise, adjourned the house, in order to prevent the excited debates which the discussion would occasion. On 11 July Marchmont presented a memorial to the queen in vindication of his conduct, and giving reasons why `it appears to be indispensably necessary that the parliament should meet upon 18 Aug., to which it is adjourned, to the end that that act which has had a first reading marked upon it may be passed' (Marchmont Papers, iii. 249). But his memorial was without effect, and he was superseded in the office of chancellor by the Earl of Seafield. In the following year he passed an act for the security of the presbyterian form of government, but aroused violent disapprobation by attempting to propose an act for settling the succession to the throne on the house of Hanover. After his dismissal from office he became one of the leaders of the squadrone party, and ultimately along with them strenuously supported the proposal for a union with England. His name appears in the list given by Lockhart of those whose support of the union was gained by a money bribe, and it was asserted that the bargain was so hardly driven that he had to return fivepence of change. Certain it is that at the time of the union the sum of 20,540l. 12s. 7d. was paid by the government to various Scottish noblemen and gentlemen, and that of this sum Marchmont received 1,104l. 15s. 7d.; but it has been plausibly argued by Sir G. H. Rose that the sum paid to Marchmont was merely arrears of his salary as lord chancellor, and of his pension (see defence in Marchmont Papers, i. pp. lxxxv-cxxxii). If this explanation be accepted, the most that can be charged against Marchmont is that he took advantage of a favourable opportunity to enforce his rightful claims. Marchmont was an unsuccessful candidate at the first election of representative peers which took place after the union, and also at the election which followed the dissolution of parliament on 15 April 1708. He was in fact too pragmatical and opinionated to win the cordial regard of any party in the state. In 1710 he was succeeded in the sheriffship of Berwick by the Earl of Home; but after the accession of George I he, as a consistent supporter of the Hanoverian succession, again came into favour, and, besides being reappointed sheriff of Berwick, was made a lord of the court of police. He, however, took no further prominent part in politics. He died at Berwick-on-Tweed on 1 Aug. 1724, and was buried in Canongate churchyard, Edinburgh. Writing about 1710 Macky, in his `Secret Memoirs,' says of him: `He hath been a fine gentleman of clear parts, but always a lover of set speeches, and could hardly give advice to a private friend without them; zealous for the Presbyterian government in Church and its Divine Right, which was the great motive that encouraged him against the crown. Business and years hath now almost worn him out; he hath been handsome and lovely, and was since King William came to the throne.' He was the author of an essay on surnames contributed to Collier's `Dictionary.'
By his wife Grisell or Grizel, daughter of Sir Thomas Ker of Cavers, Marchmont had four sons: Patrick, lord Polwarth, who, after serving through the campaigns of King William and the Duke of Marlborough, died without issue in 1710; Robert, a captain in the army, who predeceased his elder brother; Alexander, second earl of Marchmont, who assumed the surname of Campbell and is noticed under that name, and Sir Andrew Hume of Kimmerghame, a lord of session. His five daughters were: Grizel, married to George Baillie of Jerviswood [see Baillie]; Christian, died in Holland unmarried in 1688; Anne, married to Sir John Hall of Dunglass; Juliana, married to Charles Billingham; and Jean, married to Lord Torphichen.
