Markham was cashiered after eight years’ naval service in America and the West Indies, but reinstated. While on half-pay he travelled extensively. Resuming active service on the outbreak of war with France, he served in the West Indies and subsequently under St. Vincent at Cadiz and Brest, capturing several French men-of-war in theCentaur. St. Vincent snubbed him at sea, but when he became first lord of the Admiralty in Addington’s ministry, secured Markham’s appointment to the Admiralty board as one of his ‘Neptunes’. As a spokesman was needed in the House, a vacant seat was found for him before the year was out, for Portsmouth, on Admiralty recommendation to the patron Sir John Carter.
In his maiden speech, 19 Jan. 1802, Markham assured alarmists of the ability of the fleet to withstand a naval attack on Jamaica. From his own experience he advocated the setting up of courts of Admiralty in the West Indies, 24 Mar. 1802. St. Vincent procured his re-election at Portsmouth in 1802.
Markham went out of office with Addington, being listed among his followers in May and September 1804, and opposed Pitt’s second ministry. He voted against the additional force bill in June 1804 and for its repeal, 6 Mar. 1805, but spoke only on naval questions. On 1 Mar. 1805 warmly supported the continuation of the inquiry into naval abuses and he supported the vote of thanks to the commissioners, 2 May. He was spokesman for St. Vincent when his naval administration came under attack, 7, 8 May, and following the censure of Melville (which he supported, as well as his criminal prosecution) urged the House to appoint a non-partisan committee, if they intended to scrutinize St. Vincent’s conduct. The Speaker rebuked him for the implication of this. He moved for information to combat John Jeffery’s intended impeachment of St. Vincent, 16 May, and the same day supported the opposition amendment to the military commission of inquiry bill. Next day he secured the inclusion of Greenwich Hospital within the scope of the naval commissioners’ inquiry. He was dissatisfied with the prize agency bill, 28 May, and supported inquiry into the lack of timber supply, 31 May. He defended the reputation of Admiral Duckworth, under whom he had served, 7 June, and parried the attacks of Jeffery and Sir Andrew Snape Hamond on St. Vincent, 25 June, 1 July, moving for more papers to vindicate him, 3 July. He thwarted Jeffery on the same subject, 28 Jan. 1806.
Markham was restored to the Admiralty board under Viscount Howick in the Grenville ministry. Resuming his seat on 3 Mar. 1806, he spoke only in vindication of St. Vincent against Jeffery that session, notably on 14 May, when Jeffery was finally frustrated. Busy at his office from nine until six, Markham claimed he had not seen Jeffery’s charges until noon that day and had little time to prepare his answers. He voted for the repeal of Pitt’s Additional Force Act, 30 Apr. 1806, but was listed ‘adverse’ to the ministry’s abolition of the slave trade, like his brother Osborne, who sat in that Parliament. Unlike Osborne, he did not vote with the diehards against it. A few words on the navy estimates were his only contribution to the Parliament of 1806, in which he was continued at the Admiralty board by Thomas Grenville. Rumour had it that Markham was to resign because St. Vincent did not succeed Howick as first lord, and Grenville, who noted his efficiency, regretted that Markham had ‘made so many enemies’. Yet Howick assured Grenville and his brother the premier that his removal would be ‘a great misfortune to the public’ and Grenville’s other brother, the Marquess of Buckingham, pointed out that ‘though brutal’, Markham ‘at least has the advantage of knowing the details’.
Markham was reported to have voted with opposition after the dismissal of the ministry, 9 Apr. 1807, and owed his unopposed return at the ensuing election to the goodwill of Sir John Carter and not to the Admiralty.
Markham withdrew in the face of an Admiralty candidate at Portsmouth in 1818, but regained his seat in 1820. He retired for health reasons in 1826 and died at Naples, 13 Feb. 1827.
