Politics, however, proved the real business of Sackville's life. To the parliament of Queen Mary's reign which met on 20 Jan. 1557–8 he was returned both for Westmoreland and East Grinstead, and he elected to serve for Westmoreland. In the first parliament of Queen Elizabeth's reign, meeting on 23 Jan. 1558–9, he represented East Grinstead, and he represented Aylesbury in the parliament of 1563. On 17 March he conveyed a message from the house to the queen. The queen recognised his kinship with her—his father was Anne Boleyn's first cousin—and she showed much liking for him, ordering him to be in continual attendance on her. But extravagant habits led to pecuniary difficulties, and, in order to correct his ‘immoderate courses,’ he made about 1563 a foreign tour, passing through France to Italy. At Rome an unguarded avowal of protestantism involved him in a fourteen days' imprisonment. While still in the city news of his father's death—on 21 April 1566—reached him, and he hurried home to assume control of a vast inheritance.
Rich, cultivated, sagacious, and favoured by the queen, he possessed all the qualifications for playing a prominent part in politics, diplomacy, and court society. He was knighted by the Duke of Norfolk in the queen's presence on 8 June 1567, and was raised to the peerage as Lord Buckhurst on the same day. His admission to the House of Lords was calculated to strengthen the protestant party there. In the spring of 1568 he was sent to France, and, according to Cecil's ‘Diary,’ he persuaded the queen-mother to make ‘a motion for a marriage of Elizabeth with her second son, the Duke of Anjou.’ Later in the year he was directed to entertain the Cardinal Chatillon at the royal palace at Sheen, which he rented of the crown, and where he was residing with his mother. Early in 1571 he paid a second official visit to France to congratulate Charles IX on his marriage with Elizabeth of Austria. He performed his ambassadorial functions with great magnificence (cf. Holinshed, s.a. 1571), and did what he could to forward the negotiations for the queen's marriage with Anjou, privately assuring the queen-mother that Elizabeth was honestly bent on going through with the match (cf. Froude, History, ix. 368–70). Later in the year—in August—he was in attendance on Paul de Foix, a French ambassador who had come to London to continue the discussion of the marriage. On 30 Aug. he accompanied the ambassador from Audley End to Cambridge, where he was created M.A.
Buckhurst joined the privy council, and found constant employment as a commissioner at state trials. Among the many prisoners on whom he sat in judgment were Thomas, duke of Norfolk (15 Jan. 1571–2), Anthony Babington (5 Sept. 1586), and Philip, earl of Arundel (14 April 1589). Although nominated a commissioner for the trial of Mary Queen of Scots, he does not seem to have been present at Fotheringay Castle or at Westminster, where she was condemned; but he was sent to Fotheringay in December 1586 to announce to Mary the sentence of death (cf. Amias Poulet, Letter Book; Froude, xii. 219–21). He performed the painful duty as considerately as was possible, and the unhappy queen presented him with a wood carving of the procession to Calvary, which is still preserved at Knole.
Next year he once again went abroad on political service. Through the autumn of 1586 Leicester's conduct in the Low Countries caused the queen much concern, and Leicester urged that Buckhurst might be sent to investigate his action and to allay the queen's fears that he was committing her to a long and costly expedition. ‘My lord of Buckhurst would be a very fit man,’ Leicester wrote, ‘… he shall never live to do a better service’ (Leycester Correspondence, pp. 304, 378). At the end of the year Leicester came home, and in March 1587 Buckhurst was directed to survey the position of affairs in the Low Countries. His instructions were to tell the States-General that the queen, while she bore them no ill-will, could no longer aid them with men or money, but that she would intercede with Philip of Spain in their behalf. He faithfully obeyed his orders, but the queen, perceiving that it was incumbent on her to continue the war, abruptly recalled him in June. She severely reprimanded him by letter for too literally obeying his instructions. She expressed scorn of his shallow judgment which had spilled the cause, impaired her honour, and shamed himself (Motley, United Netherlands, chaps. xv. and xvi.; Froude, xii. 301). On arriving in London he was directed to confine himself to his house. For nine months the order remained in force, and Buckhurst faithfully respected it, declining to see his wife or children.
On Leicester's death he was fully restored to favour, and for the rest of her reign the queen's confidence in him was undisturbed. In December 1588 he was appointed a commissioner for ecclesiastical causes. On 24 April 1589 he was elected K.G., and was installed at Windsor on 18 Dec. Mean-