Butler, Pierce (Piers) (1652–1740), 3rd Viscount Galmoy and Jacobite earl of Newcastle, army officer, was born 21 March 1652, the son of Edward, 2nd Viscount Galmoy (c.1627–1667), and Eleanor, the daughter of Sir Nicholas Whyte of Leixlip, Co. Kildare. He succeeded to the title at the age of fifteen and was educated at Oxford (DCL 1677). In 1678 he was commissioned as a captain in Colonel Dongan's regiment, which was disbanded before he took up his post. He married Anne, daughter of Theobald Mathew of Thurles, half-brother of the 1st duke of Ormond (qv). Galmoy was appointed a privy councillor of Ireland in 1686 and lord lieutenant of Co. Kilkenny.
On the outbreak of the civil war in 1689 Galmoy was commissioned as a colonel of horse and dispatched to subdue the rebel garrison of Enniskillen. He seized Cavan and launched an unsuccessful attack on Crom castle on Upper Lough Erne, where he made up for his lack of ordinance by trundling two false cannons into the view of the defenders. He became notorious after agreeing to exchange Captain Woolstan Dixie for an Irish officer held at Crom: after the Enniskilleners had released their captive, Dixie was hanged for treason on a signpost at Belturbert. Galmoy was present at the start of the siege of Londonderry in April 1689 but returned to Dublin in May to sit in King James's parliament. He commanded his regiment at the Boyne (1 July 1690) and was present outside Limerick during the first siege (August 1690). The Williamite government in Dublin outlawed him on 11 May 1691. He commanded the reserve at the battle of Aughrim (12 July 1691) and with Patrick Sarsfield (qv) was praised for covering the Irish retreat. During the second siege of Limerick (August to September 1691) he remained with the cavalry in Co. Clare until after the ceasefire. He was a signatory to both the civil and the military treaties of Limerick (3 October 1691) and subsequently sailed to France with Sarsfield.
Galmoy continued as a colonel in King James's army until its disbandment in 1692, when his regiment was incorporated into the French army. He remained close to the Jacobite court in exile and in 1692 James created him earl of Newcastle , Co. Limerick. In 1694 he was promoted brigadier in the French army and in March 1695 he married his second wife, Henrietta Fitzjames (d. 1730), a natural daughter of James II (qv) and Isabella Churchill (sister of the duke of Marlborough) and sister of the duke of Berwick. His father-in-law appointed him gentleman of the bedchamber in 1698. He was further promoted by the French to maréchal de camp in 1702 and lieutenant general in 1705. While serving at the siege of Douai in 1712, he entered into clandestine correspondence with the 2nd duke of Ormond (qv), who then commanded the English army in Flanders, begging him to contact Berwick. Ormond changed sides after the accession of George I in 1715. Galmoy's second wife deserted him and returned to England. Galmoy died 18 June 1740 at Paris at the age of eighty-eight and was buried there. His only son (from his first marriage) had died fighting for the French at Malplaquet in 1709, leaving his attainted title to be adopted by his nephew.