Piers Butler, 3rd Viscount of Galmoye (21 March 1652 – 18 June 1740) was an Anglo-Irish nobleman and the grandson of Edward Butler, 2nd Viscount Galmoye, and his wife, Eleanor White. His father was Colonel The Honourable Piers Butler who was murdered after being taken prisoner at Lambstown, Co. Wexford after safe quarter given, in 1650. He married Elizabeth Mathew and with her had one son, Colonel Edward Butler, who was killed at the Battle of Malplaquet in 1709.

At the Glorious Revolution, he followed James II into exile in France. He commanded a regiment at the Battle of the Boyne and was taken prisoner at the Battle of Aughrim, but released after the Treaty of Limerick. He was created Earl of Newcastle in the Jacobite peerage in 1692. In France he was named Colonel of the 2nd Queen's Regiment of Irish Horse in the service of that country, and served with distinction in various battles of the War of the Spanish Succession, also becoming a Lieutenant-General in the Spanish army. After the death of his first wife, he married Henrietta FitzJames, daughter of King James II and Arabella Churchill, on 3 April 1695. The English Parliament attainted him and declared his titles forfeit in 1697. He later served in the French army as a Lieutenant-General. He was created DCL of Oxford, 6 August 1677. P.C.(Ireland), May 1686; Brigadier of Cavalry in 1694. Lord Galmoy (as he spelt his name) died in Paris on 18 June 1740 and was buried at St Paul's there.