Dartmouth, and in the company of Pepys and others, in August 1683, with a promise that he should be at home again in six weeks. His appointment was as judge-advocate of the fleet and commissioner for settling the leases of the houses between the king and the inhabitants. Pepys at once makes a note: ‘Strange to see how surprised and troubled Dr. Trumbull shows himself at this new work put on him of a judge-advocate; how he cons over the law-martial and what weak questions he asks me about it’ (Life of Pepys, 1841, i. 325–6). The expedition set sail from St. Helen's on 19 Aug. 1683, and arrived in Tangier Bay on 14 Sept. Trumbull grumbled much over the business, and complained that ‘he should have gotten ten guineas the first day of term.’ Pepys calls him ‘a man of the meanest mind as to courage that ever was born,’ and on 20 Oct. adds, with perhaps an excess of disdain, ‘So the fool went away, every creature of the house laughing at him’ (ib. i. 326–423). On 10 Nov. 1683 Trumbull returned to Whitehall. The journal of the commissioners and their report on the valuation of the properties are among Lord Dartmouth's manuscripts (Hist. MSS. Comm. 11th Rep. App. v. 97, 99, 15th Rep. App. i. 34–9).
On the promotion of Godolphin in August 1684, the king thought for a time of Trumbull as his successor in the post of secretary of state (Corresp. of Clarendon and Rochester, 1828, i. 95). Shortly afterwards he refused the office of secretary of war in Ireland, and in the following November he was presented by Lord Rochester to the king and knighted (21 Nov. 1684). On 1 Feb. 1684–5 he was made clerk of deliveries of ordnance stores. By the king's command, and much against his own inclination, he was despatched in November 1685 as envoy extraordinary to France, and, as he could not retain his post of clerk of deliveries, he accepted in lieu of it a pension of 200l. per annum, ‘the only pension he ever had.’ Sir William was a zealous opponent of Roman catholicism, and did much to benefit the condition of the English protestants in France after the revocation of the edict of Nantes. This did not commend him either to the French or English court, and in August 1686 he received letters of recall. His services to the protestants were long held in remembrance. Bayle presented to him a copy of his dictionary, and received in return a Latin letter styling the work ‘bibliothecam potius quam librum.’ Several of Bayle's friends wished him to dedicate the work to Trumbull, and Pierre Sylvestre wrote that it was rare indeed to find such a Mæcenas. Motteux dedicated to him his translation of St. Olon's ‘Present State of Morocco’ (1695), acknowledging his charity to many of the French refugees and his bounty to himself.
Through the favour of the Trelawny family, Trumbull sat from 1685 to 1687 for the Cornish borough of East Looe. In November 1686 he was made ambassador to the Porte, and embarked for Constantinople on 16 April 1687. An account of his receptions at Leghorn, Pisa, and Florence, is among the manuscripts of Mr. Cottrell Dormer (Hist. MSS. Comm. 2nd Rep. App. p. 83). He was a governor of the Hudson's Bay and the Turkey companies, and just before his departure for the East the latter body gave him ‘a dinner at the Ship at Greenwich, and presented his lady with a gold cup’ (ib. 7th Rep. App. p. 482). His mission at Constantinople, where he arrived on 17 Aug. 1687, having previously visited Smyrna and settled certain matters there, was attended by success, and at the desire of the Turkey merchants he was renominated (November 1689), and continued there until 31 July 1691. His narrative of events which occurred in Turkey to the close of April 1688 is contained in Addit. MS. 34799 (British Museum), and much of its substance was used by Sir Paul Rycaut [q. v.] in his history of the Turks, in continuation of Knolles (1700, pp. 187–290).
Trumbull was made a lord of the treasury on 3 May 1694 (ib. 14th Rep. App. ii. 550). Exactly a year later (3 May 1695) he was elevated to the position of secretary of state (in succession to Sir John Trenchard [q. v.]) and made a privy councillor; a few days afterwards he became secretary to the seven lords justices of England in the king's absence. At the general election in 1695 he was returned for the Yorkshire borough of Hedon and for the university of Oxford, when he chose the latter constituency, and sat for it until the dissolution in 1698. Trumbull, a man ‘of moderate opinions and of temper cautious to timidity … hardly equal to the duties of his great place’ (Macaulay, Hist. of England, iv. 586, v. 20), after many attempts to withdraw, resigned the seals very suddenly on 1 Dec. 1697, complaining that the lords justices had treated him ‘more like a footman than a secretary.’ Lord Ailesbury speaks of him as less than a friend, ‘nor was he to any but your obedient humble servant to all, like my Lord Plausible in the “Plain Dealer”’ (Memoirs, Roxburghe Club, ii. 373–378). One piece of Trumbull's advice to William III deserves to be recorded: ‘Do not send embassies to Italy, but a fleet into the Mediterranean.’
