Sir Henry Sidney (1529 - 5 May 1586), lord deputy of Ireland, was the eldest son of Sir William Sidney of Penshurst, a prominent politician and courtier during the reigns of Henry VIII and Edward VI, from both of whom he received extensive grants of land, including the manor of Penshurst in Kent, which became the principal residence of the family.
Henry Sidney was brought up at court as the companion of Prince Edward, afterwards King Edward VI, and he continued to enjoy the favour of the Crown, particularly throughout the reign of Queen Elizabeth I.
In 1565 Sidney was appointed lord deputy of Ireland in place of Sir Nicholas Arnold, who had succeeded the earl of Sussex in the previous year. He found the country in a more impoverished and more turbulent condition than when he left it, the chief disturbing factor being Shane O'Neill in Ulster. With difficulty he persuaded Elizabeth to sanction vigorous measures against O'Neill; and although the latter successfully avoided a decisive encounter, Sidney restored O'Neill's rival Calvagh O'Donnell to his rights, and established an English garrison at Derry which maintained some degree of order.
In 1567 Shane was murdered by the MacDonnells of Antrim, and Sidney was then free to turn his attention to the south, where with vigour and determination he arranged the quarrel between Gerald FitzGerald, 15th Earl of Desmond and Thomas Butler, 3rd Earl of Ormonde, and laid his hand heavily on other disturbers of the peace; then, returning to Ulster, he compelled Turlough Luineach O'Neill, Shane's successor in the clan chieftainship, to make submission, and placed garrisons at Belfast and Carrickfergus to overawe Tyrone and the Glynns.
In pursuance of this policy Sidney proposed the appointment of a military governor ("Lord President") in the provinces of Munster and Connaught. This provoked the first of the Desmond Rebellions led by James Fitzmaurice Fitzgerald of the Geraldine family, which had been put down with great severity by 1573. Sidney dealt severely with the unruly Butlers in Ormond and Kilkenny, who had risen out in defiance of the government in reaction to the opportunistic claims to certain of their lands by Sir Peter Carew, a rather rough gentleman from Devon who pursued his entitlement with the blessing of the Dublin administration. At Kilkenny large numbers of Sir Edmund Butler's followers were hanged, and three brothers of Thomas Butler, 3rd Earl of Ormonde, were attainted by an act of the Irish parliament in 1570.
Sidney left Ireland in 1571, aggrieved by the slight appreciation of his statesmanship shown by the queen; but he returned in September, 1575 with increased powers and renewed tokens of royal approval, to find matters in a worse state than before, especially in Antrim, where the MacQuillans of the Route and Sorley Boy MacDonnell were the chief fomenters of disorder. Having to some extent pacified this northern territory, Sidney repaired to the south, where he was equally successful in making his authority respected. He left his mark on the administrative areas of the island by perfecting certain shire divisions on the English model.
At an earlier period he had already in the north combined the districts of the Ardes and Clandeboye to form the county of Carrickfergus, and had converted the country of the O'Farrells into the County Longford. He then carried out a similar policy in Connaught, where the ancient Irish district of Thomond became County Clare, and the counties of Galway, Mayo, Sligo and Roscommon were also delimited.
Sidney also suppressed a rebellion headed by the earl of Clanricarde and his sons in 1576, and hunted Rory O'More to his death two years later. Meantime Sidney's annual levy (the cess), which was designed to fund a central government militia, had caused discontent among the gentry of the Pale, who carried their grievances to queen Elizabeth. Greatly to Sidney's chagrin the queen censured his extravagance, and notwithstanding his distinguished services to the Crown he was recalled in September 1578, and was coldly received by Elizabeth.
He lived chiefly at Ludlow Castle for the remainder of his life, performing his duties as president of the Welsh Marches.