After short periods as President of the Council of State and Treasurer of the Navy, he served as Lord Privy Seal between 1673 and 1682 for Charles II.

Having made the grand tour he returned to Ireland; and being employed by Parliament on a mission to the Duke of Ormonde, now reduced to the last extremities, he succeeded in concluding a treaty with him on 19 June 1647, thus securing the country from complete subjection to the rebels.

[1] Anglesey supported the king's administration in parliament, but opposed strongly the unjust measure which, on the abolition of the Court of Wards and Liveries, placed the extra burden of taxation thus rendered necessary on the Excise.

In February 1661 he had obtained a captaincy of horse, and in 1667 he exchanged his post of Vice-Treasurer of Ireland with Sir George Carteret for that of Treasurer of the Navy.

This same year his naval accounts were subjected to an examination in consequence of his indignant refusal to take part in the attack upon Ormonde;[8] and he was suspended from his office in 1668, no charge, however, against him being substantiated.

On 6 December he protested with three other peers against the measure sent up from the Commons enforcing the disarming of all convicted recusants and taking bail from them to keep the peace; he was the only peer to dissent from the motion declaring the existence of an Irish plot; and though believing in the guilt and voting for the death of Lord Stafford, he interceded, according to his own account,[11] with the king for him as well as for the barrister Richard Langhorne and Oliver Plunkett, Roman Catholic Archbishop of Armagh and Primate of All Ireland.

[12] His independent attitude drew upon him an attack by the notorious informer Dangerfield, and in the Commons by the Attorney General, Sir William Jones, who accused him of endeavouring to stifle the evidence against the Romanists.

In 1682 he wrote The Account of Arthur, Earl of Anglesey ... of the true state of Your Majesty's Government and Kingdom, which was addressed to the king in a tone of censure and remonstrance, but appears not to have been printed till 1694.

He divided his time between his estate at Blechingdon in Oxfordshire, and his house on Drury Lane in London, where he died in 1686 from quinsy,[2] closing a career marked by great ability, statesmanship and business capacity, and by conspicuous courage and independence of judgement.

The sale was interrupted by the overseer of the press, Sir Roger L’Estrange, to withdraw controversial materials which included the removal of works by John Milton.

[12] Anglesey married Elizabeth, daughter and co-heiress of Sir James Altham of Oxey, Hertfordshire, a baron of the Exchequer, and his first wife Margaret Skinner.

He was summoned to the Irish House of Peers as Viscount Valentia, but was denied his writ to the parliament of Great Britain by a majority of one vote.