On 27 May 1648 the greater part of the parliamentary fleet in the Downs revolted to the king, and two days later parliament reappointed Warwick to the post of lord high admiral, in the hope that his popularity would secure the fidelity of the sailors. He went on board at once, and finding, after some futile negotiations, that it was impossible to win back the crews of the nine revolted ships, devoted himself to getting together a new fleet and discharging disaffected sailors and officers (Lords' Journals, x. 290, 297, 313, 355, 414). By the end of August Warwick felt strong enough to offer battle to Prince Charles and the revolted ships off the mouth of the Medway, but a storm prevented the intended action, and want of provisions obliged Prince Charles to retreat to Holland without fighting (ib. x. 483, 488, 494). Warwick blockaded the prince's ships in Helvoetsluys in September, remaining off the Dutch coast till the end of November, when the winter weather obliged him to return to England (ib. x. 522, 595, 625; Gardiner, Great Civil War, iv. 210). He had succeeded in regaining four of the prince's fleet, and in preventing the rest from preying upon English trade, while restoring the spirit and the discipline of the parliamentary fleet. A pamphlet impugning his fidelity to parliament gave him an opportunity of summing up his services (A Declaration of the Earl of Warwick in answer to a Scandalous Pamphlet, &c., 1648, 4to).
Nevertheless, the abolition of the monarchy and the House of Lords was a measure too extreme for Warwick to approve, nor could the independents leave the control of the fleet in his hands. On 23 Feb. 1649 parliament repealed the act constituting Warwick lord high admiral, and transferred the government of the navy to the council of state. His interposition on behalf of the life of his brother, the Earl of Holland, met with no success (Clarendon, Rebellion, xi. 504). Therefore, while not actively hostile to the republic and its governors, Warwick took no part in public affairs during the Commonwealth. When Cromwell became protector, however, Warwick gave him both support and encouragement. At Cromwell's second inauguration (26 June 1657) Warwick bore the sword of state before the Protector and helped to invest him in his robe of purple velvet (Cromwelliana, p. 165). The marriage of Cromwell's daughter Frances with Warwick's grandson and heir, Robert Rich (14 Nov. 1657), gave a still clearer proof of Warwick's feelings towards the Protector (ib. p. 159; Hist. MSS. Comm. 5th Rep. p. 177; Thurloe, vi. 573). Robert Rich died on 16 Feb. 1658 (ib. vi. 820). In his touching answer to the Protector's letter of condolence, Warwick ended by congratulating Cromwell on his ‘prudent, heroic, and honourable management’ of public affairs. ‘Others goodness is their own; yours is a whole country's, yea three kingdoms, for which you justly possess interest and renown: with wise and good men virtue is a thousand escutcheons. Go on, my lord, go on happily, to love religion, to exemplify it. May your lordship long continue an instrument of use, a pattern of virtue, and a precedent of glory’ (Godwin, Hist. of the Commonwealth, iv. 530).
Warwick died on 19 April 1658, and was buried at Felsted, Essex, on 1 May. Clarendon says that he was extremely lamented by Cromwell, and adds that he ‘left his estate, which before was subject to a vast debt, more improved and repaired than any man who trafficked in that desperate commodity of rebellion’ (Rebellion, vi. 404, xv. 145). Clarendon's view that Warwick was a jovial hypocrite is scarcely borne out by other contemporary evidence. The ‘jollity and good humour’ which he mentions are indeed confirmed. ‘He was one of the most best-natured and cheerfullest persons I have in my time met with,’ writes his pious daughter-in-law (Autobiography of Lady Warwick, ed. Croker, p. 27). Edmund Calamy, however, in his sermon at Warwick's funeral, enlarges on his zeal for religion; and Warwick's public conduct during all the later part of his career is perfectly consistent with Calamy's account of his private life (A Pattern for All, especially for Noble Persons, &c., 1658, 4to, pp. 34–9).
Vandyck's portrait of Warwick was engraved by Houbraken and Vertue. There are also engraved portraits by Hollar and Faithorne, while Ricraft, in his ‘Survey of England's Champions,’ 1647, and Vicars in ‘England's Worthies,’ 1647, both give portraits and memoirs of Warwick.
Warwick was three times married: first, to Frances, daughter of Sir William Hatton, knt., 24 Feb. 1605 (Winwood Papers, iii. 49); she died in August 1634. Secondly, Susan, daughter of Sir Rowe Rowe, lord mayor of London in 1607, and widow of William Halliday, alderman of London; she died on 16 Jan. 1645–6, and was buried at St. Lawrence's Church, near the Guildhall in London (Autobiography of Mary, Countess of Warwick, p. 15; Wheatley and Cunningham, London Past and Present, iii. 450). Thirdly, Eleanor, daughter of Sir Edward Wortley, and Dowager Countess of Sussex, on 30 March 1646. Many of this lady's letters are given in the