The control of foreign affairs was entrusted to him, and he was chiefly responsible for the attack on the Smyrna fleet and for the Second Anglo-Dutch War,[1] during which he married the beautiful (and Dutch) Isabella van Nassau-Beverweert (28 December 1633 – 18 January 1718) in March 1665.

[1] On the death of Thomas Wriothesley, 4th Earl of Southampton, whose administration he had attacked, his great ambition, the treasurership, was not satisfied; and on the fall of Clarendon, against whom he had intrigued, he did not, though becoming a member of the Cabal Ministry, obtain the supreme influence which he had expected; for Buckingham first equalled, and soon surpassed him, in the royal favour.

With Buckingham a sharp rivalry sprang up, and they only combined forces when endeavouring to bring about some evil measure, such as the ruin of the great Ormonde, who was an opponent of their policy and their schemes.

[1] He supported several other measures—the scheme for rendering the king's power absolute by force of arms; the "stop of the exchequer", involving a repudiation of the state debt in 1672; and the Royal Declaration of Indulgence the same year, "that we might keep all quiet at home whilst we are busy abroad."

On 22 April 1672 he was created an earl, with a special remainder that the title would pass to his daughter, and on 15 June obtained the Order of the Garter; the same month he proceeded with Buckingham on a mission, first to William at The Hague, and afterwards to Louis at Utrecht, endeavouring to force upon the Dutch terms of peace which were indignantly refused, failing to end the Third Anglo-Dutch War.

But Arlington's support of the court policy was entirely subordinate to personal interests; and after the appointment of Clifford in November 1672 to the treasurership, his jealousy and mortification, together with his alarm at the violent opposition aroused in parliament, caused him to veer over to the other side.

[1] He advised Charles in March 1673 to submit the legality of the declaration of indulgence to the House of Lords, and supported the Test Act of the same year, which compelled Clifford to resign.

He joined the pro-Dutch party, and in order to make his peace with his new allies, disclosed the secret treaty of Dover to the staunch Protestants Ormonde and Anthony Ashley-Cooper, 1st Earl of Shaftesbury.

On 15 January 1674 he was impeached by the Commons, the specific charges being "popery", corruption, and the betrayal of his trust – Buckingham in his own defence having accused him the day before of being the chief instigator of the French and anti-Protestant policy, of the scheme of governing by consent.

In 1675 he made another attempt to gain favour with the parliament by supporting measures against France and against the Roman Catholics, and by joining in the pressure put upon Charles to remove James from the court.

It was safe to ridicule his person and behaviour, and it became a common jest for "some courtier to put black patch upon his nose and strut about with a white staff in a hand in order to make the king merry at his expense".