cond Earl of Marchmont], by his wife Margaret, daughter and heiress of Sir Alexander Campbell of Cessnock, Ayrshire, was born on 15 March 1708. He and his brother Alexander, who died lord clerk register in 1756, were twins, and so closely resembled each other in their persons that even during manhood they were frequently mistaken for one another by their most intimate friends. Being both destined for the profession of law, they were both sent, as their father had been, to complete their education in Holland, where they studied successively at Utrecht and Franeker. At the general election of 1734, when their father, through the hostility of Walpole, failed to be chosen a representative peer for Scotland, the two brothers entered parliament, Hugh, who was known as Lord Polwarth, as member for the town of Berwick, and Alexander as member for the county. Partly in requital of Walpole's treatment of their father, partly owing to dislike of Walpole's policy, they became his persistent and relentless opponents. Lord Polwarth's trenchant attacks on Walpole elevated him at once to the position of a leader of the opposition. Smollett, referring to his first appearance in the debates of the House of Commons, describes him as a ‘nobleman of elegant parts, keen penetration, and uncommon sagacity, who spoke with all the fluency and fervour of elocution.’ Walpole himself estimated Polwarth's powers of attack at their just value, and declared that there were few things he more ardently desired than to see him at the head of his family, and thus no longer eligible for a seat in the commons. When Walpole's sons were praising the speeches of Pulteney, Pitt, Lyttelton, and others, he answered, ‘You may cry up their speeches if you please, but when I have answered Sir John Barnard and Lord Polwarth I think I have concluded the debate’ (note to Coxe's Walpole).
On the death of his father on 27 Feb. 1740, Hume became third Earl of Marchmont. Removed from the House of Commons, and unable to get elected as a representative peer, he was precluded from continuing the political career which had opened so promisingly. His political ally, Sir William Wyndham, died on 17 June following. ‘What a star has our minister!’ (Walpole), Bolingbroke wrote to Pope: ‘Wyndham dead, Marchmont disabled—the loss of Marchmont and Wyndham to our country’ (Marchmont Papers, ii. 224). Pope himself told Marchmont that ‘if God had not given this country to perdition he would not have removed from its service the man whose capacity and integrity alone could have saved it’ (ib. p.208). Marchmont succeeded to Wyndham's place in Bolingbroke's intimacy, and during the latter's closing years was his most confidential friend. For some time he occupied Bolingbroke's house at Battersea. Bolingbroke wrote to him that he preferred to be remembered by posterity as ‘Wyndham's and Marchmont's friend’ rather than in any other character (ib. ii. 230). Pope immortalised his intimacy with Marchmont in the inscription on the grotto at Twickenham, ‘There the bright flame was shot through Marchmont's soul.’ While excluded from devoted much attention to husbandry, forestry, and gardening, in which he acquired the reputation of possessing exceptional knowledge and skill. He was also a very accomplished horseman. He built Marchmont House, Berwickshire.
Marchmont was one of Pope's four executors. He is blamed by Johnson for having along with Bolingbroke consented to the destruction of Pope's unpublished manuscripts and papers. But Pope in his will left his papers to Bolingbroke, who was not one of his executors, ‘committing them to his sole care and judgment to preserve or destroy them, or, in case he should not survive him, to the above said Earl of Marchmont.’ As Bolingbroke survived Pope, the papers did not come into Marchmont's possession, although it is possible that Bolingbroke consulted him regarding their destruction. Pope in his will left Marchmont a large-paper edition of ‘Thirannus’ and a portrait of Bolingbroke by Richardson. Marchmont was also one of the executors of Sarah, duchess of Marlborough, who died in the same year as Pope. She had been the friend of Marchmont's father, and her relations were equally cordial with the son, to whom she left 2,000l.
Marchmont, on the publication of Johnson's ‘Life of Pope,’ complained that Johnson made erroneous statements in spite of information with which he had supplied him. The truth seems to have been that when Johnson was writing his ‘Life of Pope’ Boswell, without consulting Johnson, communicated with Marchmont as to his knowledge of Pope (12 May 1779), and that Marchmont made an offer of assistance which was declined by Johnson. In 1780, however, Johnson visited Marchmont at his house in Curzon Street, discussed the subject, and expressed much satisfaction with the interview. Further information of value was afterwards supplied by Marchmont to Boswell, but was rejected by Johnson.
The formation of the ‘Broad Bottom’ administration in 1744 under his friend Chesterfield and Pitt enabled Marchmont to re-enter political life. During the rebellion of 1745