Savile succeeded to the English peerage at his father's death on 31 Aug. 1630. On the same day he endeavoured to seize some property his father had left to his sister, Mrs. Anne Leigh, and compelled the tenant to sign a deed with a dagger at his breast (Hist. MSS. Comm., 4th Rep. App. p. 79; Cal. State Papers, Dom. 1637, p. 481). He was also accused of tampering with the depositions of the witnesses. These proceedings led to his trial in the Star-chamber and to his imprisonment in the Fleet (ib. 1638–9, p. 228). This, combined with his hostility to Strafford, made Savile a bitter enemy of the government. In the spring of 1640 he visited John Campbell, first earl of Loudoun [q. v.], one of the Scots commissioners who had been imprisoned in the Tower. Through Campbell, Archibald Johnston (afterwards called Lord Warriston) [q. v.] addressed on 23 June to Savile, ‘as the recognised organ of the English malcontents’ (Gardiner, ix. 178), a letter in which he expressed the desire of the Scots for a definite understanding with the English nobility, and asked for a special engagement from some principal persons that they would join the invading army when it entered Northumberland, or send money for its support. On 8 July Savile forwarded a reply signed by Bedford, Essex, Brooke, Warwick, Scrope, Mandeville, and himself, refusing to commit any treasonable act, but promising to stand by the Scots in a legal and honourable way. At the same time Savile sent an answer on his own account, making unqualified offers of aid. The Scots were not satisfied, and a few weeks later Savile forwarded an open declaration and engagement in their favour; appended were the signatures of the six peers, which Savile himself forged with remarkable skill (for a discussion of the genuineness of the letter as printed by Oldmixon, see Gardiner, Hist. of England, ed. 1892, ix. 179 n.). On 3 Oct. following Savile acknowledged the forgery, pleading that he had acted on patriotic motives, and on this ground it was condoned.
On 28 Aug. Savile signed the peers' petition calling for a parliament, and in September he was appointed commissioner to treat with the Scots at Ripon (cf. Notes of the Treaty of Ripon, Camden Soc.). On 19 Feb. 1640–1 he was sworn of the privy council, and in April he was given the custody of New Park and Sheriffhutton Park, formerly held by Strafford. He was also made lord president of the council of the north and lord lieutenant of Yorkshire, in succession to Strafford; but parliament abolished the former office in August, and forced the king to confer the latter on Essex. These promotions and the fall of Strafford won Savile over to the court, and, in ‘recompense of his discovery of the treasons and conspiracies’ (Clarendon) of the popular party, he was promised Vane's office of treasurer. He was one of the witnesses against Strafford at his trial, and persuaded Charles to declare that he had no wish to restore the earl to any place of authority; but when the bill of attainder came before the House of Lords, he objected to it as infringing their privileges. He was appointed a commissioner of regency on 9 Aug. 1641, and treasurer of the household on 26 Nov. On 21 Jan. 1641–2 the king placed him on a commission to inquire into royal revenues and expenses. In May he conveyed to parliament the king's reply to the charges about the army plot, and in June he offered the king a force of fifty horse. Early in the same month he prevented the presentation of an anti-royalist petition by the people of Yorkshire (cf. A copy of Letter from Sir Jno. Bourchier, London, 1642). For his action on this occasion he was on 6 June declared incapable of sitting in parliament and a public enemy (Hist. MSS. Comm. 5th Rep. App. p. 27).
Alarmed by this proceeding, Savile once more sought to make his peace with parliament. He wrote in November 1642 a long vindication of his conduct (Cal. State Papers, 1642, pp. 411 et seq.; Papers relating to the Delinquency of Lord Savile, Camden Soc. pp. 1–4), stating that he was compelled to attend the king by his duties as treasurer; that he had urged moderation on him, and drawn up the royal message investing parliament with the control of the militia; that he had refused to join the king when he raised his standard at Nottingham, or to take any command in the royalist army, but retired to his own house and occupied himself with protecting ministers and others from violence. In the same month Captain John Hotham [q. v.] appeared before Howley Hall, and Savile entered into negotiations with him; in return for the payment of 1,000l. Hotham promised Savile the protection of parliament. Soon afterwards the parliamentarians retreated before Newcastle, the royalist general. The latter got wind of Savile's composition, and was also informed that he was privy to a plot to seize Henrietta Maria on her way from the coast to York. He accordingly sent two hundred horsemen, who seized him one night and shut him up in Newark Castle. There Savile remained for six months. Meanwhile Newcastle pillaged Howley Hall and forwarded the