Sir Henry Mildmay (ca. 1593–1668) was an English politician who sat in the House of Commons at various times between 1621 and 1659. He supported the Parliamentarian cause in the English Civil War and was one of the Regicides of Charles I of England.
Mildmay was knighted in 1617 and made Master of the Jewel Office in 1618. In 1621, Mildmay was elected Member of Parliament for Maldon. He was elected MP for Westbury in 1624 and Maldon again in 1625 and 1628. He sat until 1629 when King Charles decided to rule without parliament for eleven years He attended Charles I on a visit to Scotland in 1639.
In April 1640 Mildmay was elected MP for Maldon in the Short Parliament. He was re-elected MP for Maldon in the Long Parliament in November 1640 He supported parliament during the Civil War and was a revenue commissioner between 1645 and 1652. In 1646 he was left as hostage in Scotland. He remained in the Rump Parliament after Pride's Purge and was present at the trial of Charles I.
Mildmay was a member of the Councils of State from 1649 until 1652. He was called on to account for the king's jewels in 1660 and attempted to escape. He was disgraced and sentenced to imprisonment for life. In 1664 a warrant was issued for his transportation to Tangier, where he died four years later.
Mildmay was second son of Humphrey Mildmay (d. 1613) of Danbury Place, Essex, by Mary (1560–1633), daughter of Henry Capel of Little Hadham, Hertfordshire, He was brought up at court, and excelled in all manly exercises. Clarendon terms him a "great flatterer of all persons in authority, and a spy in all places for them", On 9 August 1617 Mildmay, being then one of the king's sewers, was knighted at Kendal. In 1619 he made a wealthy match, through the king's good offices, and bought Wanstead House, Essex, of the George Villiers, Marquis of Buckingham, where he entertained James I in June of that year.