Henry Sydney (or Sidney), 1st Earl of Romney (8 April 1641 – 8 April 1704) was born in Paris, a son of Robert Sidney, 2nd Earl of Leicester, of Penshurst Place in Kent, England, by Lady Dorothy Percy, a daughter of Henry Percy, 9th Earl of Northumberland and sister of Algernon Percy, 10th Earl of Northumberland.
Henry was a brother of Philip Sidney, 3rd Earl of Leicester, who was born in 1619; Algernon Sydney, the Republican martyr, who was born at Penshurst Place in 1622 but was executed, having been found party to the "Rye House Plot" 1683; and Robert Sidney. His sister was Dorothy Spencer, Countess of Sunderland.
Henry entered Parliament in 1679 and, as a statesman, was one of the Immortal Seven (the author of the letter, in fact) to invite the Protestant William III of Orange to take the throne through the Glorious Revolution, when King James II was deposed under legislation passed to exclude Charles II's Catholic brother (the Duke of York) from the succession. King William created Sydney Baron Milton and Viscount Sydney in 1689.
He was present at the Battle of the Boyne in 1690, and was later to become employed by King William as envoy to the Hague and also served as Lord Lieutenant of Ireland for the period between 1692 and 1693 and was created Earl of Romney in 1694, but began to lose favour at the court under Queen Anne.
Henry Sidney served as Master-General of the Ordnance from 1693 to 1702. Additionally, he was a Lieutenant-General and Colonel of the First Regiment of Foot Guards, (Grenadier Guards). He employed the Sidney family emblem on prison uniforms, and other government property.
He died unmarried, in London, 'a proud but drunken man' aged 63.
The University of Nottingham Library is in possession of the catalogue of the papers of Hans William Bentinck, 1st Earl of Portland which outline much of Sidney’s correspondence.
There further have survived 98 letters between Sidney and George Legge, 1st Baron Dartmouth, which include papers written by Dartmouth during his confinement at the Tower.