1587 he and other border chiefs were summoned to appear before the privy council on 9 June to answer ‘touching good rule and quietness to be observed on the borders hereafter, under pain of treason’ (ib. p. 183); and on the 9th Robert Scott gave caution for him in five thousand merks that he would appear on the 21st (ib. p. 189). Towards the close of the year he and the laird of Cessford were, however, committed to ward for making incursions in England (Calderwood, History, iv. 641); but on 13 Dec. he found caution in 10,000l. that on being liberated from the castle of Edinburgh he would by 10 Jan. find surety for the relief of the king and his wardens of ‘all attempts against the peace of England bygone and to come’ (Reg. P. C. Scotl. iv. 234).
On the occasion of the queen's coronation, 17 May 1590, Buccleuch was dubbed a knight (Calderwood, History,, v. 95). When his stepfather, Bothwell, was put to the horn in the following year, he was appointed keeper of Liddesdale, and on 6 July, with the border chiefs, he gave his oath to concur without ‘shrinking, shift, or excuse in Bothwell's pursuit’ (Reg. P. C. Scotl. iv. 649), a band to this effect being also subscribed by him at Edinburgh on 6 Aug. (ib. p. 667). Hardly had it been subscribed when the pursuit of Bothwell was declared to be unnecessary; but doubts of Buccleuch's fidelity being nevertheless entertained, he next day gave caution in 10,000l. that he would go abroad within a month, and not return within the next three years (ib. p. 668); and on 29 Aug. he was relieved of the keepership of Liddesdale (ib. p. 674). He, however, obtained letters permitting his return to Scotland on 12 Nov. 1592 (Fraser, Scotts of Buccleuch, ii. 250). On 22 May 1594 he was named one of a commission for the pursuit of Bothwell (Reg. P. C. Scotl. v. 137), and at ‘the king's earnest desire’ he was in October following reappointed to the office of keeper of Liddesdale ‘heritably in time to come’ (ib. p. 178). On the division of Bothwell's lands after his flight to France in 1595, Buccleuch obtained the lordship of Crichton and Liddesdale (Calderwood, v. 363). As a follower of the Hamiltons he in the same year joined them in the league with the chancellor Maitland against Mar. The queen proposed that he should succeed Mar in the guardianship of the young prince, and when the king declined to accede to this arrangement, Buccleuch, with the bold recklessness of the borderer, proposed that both king and prince should be seized, and that, this being done, Mar should be arraigned for high treason; but the proposal was too much for the prudent chancellor. In the following year Buccleuch won lasting renown by his brilliant exploit in delivering Kinmont Willie [see Armstrong, William, (fl. 1596)] from Carlisle Castle. Not only was the achievement noteworthy for its clever daring; it indicated the faculty of swift decision, and the high moral courage of a strong personality. Persuaded that he had justice on his side, Buccleuch never hesitated to defy all consequences. His simple, and to himself unanswerable, plea was that Armstrong, having been captured during a truce, was not legally a prisoner. It was scarcely to be expected, however, that Elizabeth would homologate this novel method of rectifying her representative's mistake, or that she would regard the deed as aught else than an illegal outrage committed by the king of Scotland's representative, and thus virtually in his name. In accordance with Elizabeth's instructions, Bowes, her representative, made formal complaint against it before the Scottish parliament, and concluded a long speech by declaring that peace could no longer exist between the two realms unless Buccleuch were delivered into England to be punished at the queen's pleasure. Although Buccleuch asserted that the illegality was chargeable only against the English warden (Armstrong not being in any proper sense a prisoner), he declared his readiness to submit his case to a joint English and Scottish commission. But the sympathy of the Scots being strongly with him, it was only after repeated and urgent demands by Elizabeth that arrangements were entered into for its appointment, and before it met Buccleuch still further exasperated Elizabeth by a raid into England, in which he apprehended six Tyndale rievers, whom he put to death. Consequently the commission which met at Berwick decided that he should enter into bond in England until pledges were given for the future maintenance of peace. He therefore surrendered himself to Sir William Selby, master of the ordnance at Berwick, on 7 Oct. 1597. On 12 May 1599 he received from Elizabeth a safe-conduct to pass abroad for the recovery of his health, and in 1600 he was in Paris, when he gave evidence before the Cour des Aides in regard to the genealogy of one Andrew Scott, Sieur de Savigne (Fraser, Scotts of Buccleuch, i. 172–3).
After the accession of James VI to the throne of England, Buccleuch in 1604 raised a regiment of the borderers, in command of whom he distinguished himself under Maurice, prince of Orange, in the war against the Spaniards in the Netherlands. On 4 March 1606 he was raised to the peerage by the
