After the king's death Robartes took no further part in public affairs, and abstained from sharing in the plots against the republic. He seems to have been less hostile to the protectorate, for at Cromwell's second installation the train of the Protector's purple robe was borne by the son of Robartes (Ludlow, Memoirs, ii. 29). At the Restoration his influence with the presbyterian party, and the support of Monck, secured him a place in the government. He was admitted to the privy council (1 June 1660), appointed a commissioner of the treasury (19 June–8 Sept. 1660), and made lord deputy of Ireland (25 July 1660; Ranke, Hist. of England, v. 526; Doyle, iii. 91). Clarendon, discussing the reasons which led to the choice of Robartes for the post of lord deputy, characterises him as ‘a man of more than ordinary parts, well versed in the knowledge of the law, and esteemed of integrity not to be corrupted by money. But he was a sullen, morose man, intolerably proud, and had some humours as inconvenient as small vices, which made him hard to live with’ (Continuation of Life, pp. 125–8; cf. Burnet, Own Time, i. 178; Pepys, Diary, 2 March 1664). The choice was not a happy one, for Robartes proved obstructive in matters of business, quarrelled with the representatives of the Irish nobility, and, feeling himself aggrieved because he was merely the deputy and Monck the lord lieutenant, refused to go to Ireland. As he had great parliamentary influence, ‘for of all who had so few friends he had the most followers,’ the king thought better to induce him to resign the deputyship by giving him the post of lord privy seal (18 May 1661; ib. pp. 198–200).
Robartes had been suspected of being too much inclined to presbyterianism, but he had purged himself of the charge, protesting ‘that he believed episcopacy to be the best government the church could be submitted to.’ This did not prevent him from becoming the most active advocate of a policy of toleration towards nonconformists. On 23 Feb. 1663 he introduced a bill for enabling the king to dispense with the act of uniformity and other statutes by granting licenses to peaceable protestant nonconformists for the exercise of their religion. The bill was so strongly opposed that it was ultimately dropped. Robartes was from that time closely associated with Clarendon's opponents, and is mentioned by Ruvigny as sparing no pains to undermine the chancellor's influence with the king (ib. p. 583; Christie, Life of Shaftesbury, i. 267–73, App. p. lxxix). He continued to hold the office of lord privy seal till 22 April 1673, and on 3 May 1669 was appointed lord lieutenant of Ireland in place of the Duke of Ormonde. Ludlow refers to this appointment as showing the triumph of ‘the honestest party of those about the king.’ Carte regards it as the victory of Ormonde's personal enemies, and a preliminary step to his accusation. Robartes, however, could find no grounds for accusing Ormonde, and was himself criticised as slothful in business, and wanting both in temper and affability. He was recalled in May 1670 (Ludlow, Memoirs, ed. 1894, ii. 495; Carte, Ormonde, iv. 355–8, ed. 1851).
When Charles II reorganised the privy council on Sir William Temple's plan, Robartes was one of the new body (21 April 1679), and on 23 July following he was created Viscount Bodmin and Earl of Radnor. On 25 Oct. 1679 he was further appointed lord president of the council. Roger North terms him ‘a good old English lord,’ who, disgusted by the violence of the whigs, had abandoned the cause of the opposition, and, ‘notwithstanding his uncontrollable testiness and perverse humours, did the king very good service’ (Lives of the Norths, ii. 54, ed. 1826). He also did good service to the Duke of York by his opposition to the passing of Monmouth's patent (Manuscripts of the Earl of Dartmouth, p. 33). Robartes continued president of the council till August 1684, and offered no opposition to the arbitrary measures which marked the close of Charles II's reign. Burnet, speaking of his supersession by Rochester, says ‘he had for some years acted a very mean part, in which he had lost the character of a steady, cynical Englishman, which he had maintained in the former course of his life’ (Own Time, ii. 444, ed. 1833). He died on 17 July 1685 (Luttrell, Diary, i. 315, 354; Wood, Athenæ, iv. 178). A portrait of Robartes was No. 741 in the national portrait exhibition of 1868.
Robartes was the author of: 1. ‘A Discourse of the Vanity of the Creature, grounded on Eccles. i. 2,’ London, 1673, 8vo. 2. ‘Some volumes of Notes on the Proceedings of the House of Lords, and Miscellaneous Memoranda occasionally referred to as his Memoirs’ (Harleian MSS. 2224, 2237, 2243, 2325, 5091–5). Excepting one or two anecdotes, they contain nothing of interest (cf. Sanford, Studies and Illustrations of the Great Rebellion, pp. 291, 496).
Robartes married twice: first, Lucy Rich, second daughter of Robert, second earl of Warwick; secondly, Letitia Isabella (d. 1714), daughter of Sir John Smith of Bidborough, Kent, knight. This lady has been identified with the ‘Lady Robarts’ mentioned