[6] Clarendon terms him a "great flatterer of all persons in authority, and a spy in all places for them",[7] On 9 August 1617 Mildmay, being then one of the king's sewers, was knighted at Kendal.
[8] In 1619 he made a wealthy match, through the king's good offices,[9] and bought Wanstead House, Essex, from George Villiers, Marquis of Buckingham, where he entertained James I in June of that year.
[15] In parliament he took part in the great debate on the foreign policy of the crown, 6 August 1625, when, as a friend of Buckingham, he proposed a vote of money for completing the equipment of the fleet against Spain.
[16] On 5 May 1627, King Charles I, suspended a statute of Emmanuel College, Cambridge, for the removal of fellows at the time of commencing doctors, or within one year thereafter.
Sir Henry being anxious, as grandson of the founder, to maintain the statute, offered to annexe five or six new benefices to the college within six years, and thus obtained its revocation.
[25] In November 1643, he got into trouble with parliament by saying of Philip, Lord Wharton, who had raised a regiment for the parliamentary service,[26] and subsequently became a member of the council of state,[27] "that he had made his peace at Oxon, and therefore was not fit to be entrusted with any public trust".
(It was not he but a cousin Sir Henry Mildmay of Woodham Walters and Moulsham who on 17 June 1645 vainly claimed, by petition, the barony of Fitzwalter;[29] From 1645 to 1652, he was a commissioner for the revenue.
[33] He was a member of the councils of state elected in 1649, 1650, 1651, and 1652, and sat on the committee appointed to consider the formation of a West India Company, and the regulation of the fishing upon the British coasts.
[36] Thenceforward he ceased to take a prominent part in affairs, though he signed the remonstrance promoted on 22 September 1656 by Sir Arthur Hesilrige on behalf of the excluded members.
[37] On 15 May 1660, Sir Henry was ordered, to attend the committee appointed to consider Charles II's reception, and give an account of the whereabouts of the crowns, robes, sceptres, and jewels belonging to the King.
He attempted to escape abroad, but was seized by Lord Winchelsea at Rye, Sussex, and was excepted out of the General Pardon Bill.
On 1 July 1661 he was brought to the bar of the House of Commons, and after evidence had been produced against him, and he had been made to confess his guilt, he was degraded from his honours and titles.
[38] In a petition to the House of Lords, dated 25 July, he prayed for commiseration, alleging that he was present at the trial only to seek some opportunity of saving the king's life.