Endymion Porter (1587–1649) was an English diplomat and royalist.
He was descended from Sir William Porter, sergeant-at-arms to Henry VII, and son of Edmund Porter, of Aston-sub-Edge in Gloucestershire, by his cousin Angela, daughter of Giles Porter of Mickleton, in the same county.
He was brought up in Spain—where he had relatives—as page in the household of Olivares. He afterwards entered successively the service of Edward Villiers and of Buckingham, and through the latter's recommendation became groom of the bedchamber to Charles I.
In October 1622 he was sent to negotiate concerning the affairs of the Electorate of the Palatinate and the proposed "Spanish Match" of the Prince of Wales with the Infanta. He accompanied Charles and Buckingham on their foolhardy expedition in 1623, acted as their interpreter, and was included in the consequent attack made by Lord Bristol on Buckingham in 1626.
In 1628 he was employed as envoy to Spain to negotiate for peace, and in 1634 on a mission to the Netherlands to the Cardinal-Infante Ferdinand.
Porter was one of the promoters of the 1635 Courteen association.
During the Civil War Porter remained a constant and faithful servant of the king. He was with him during the two Scottish campaigns, attended him again on the visit to Scotland in August 1641, and followed Charles on his last departure from London in 1642, receiving the nominal command of a regiment, and sitting in the Royalist parliament at Oxford in 1643.