Oliver FitzWilliam, 1st Earl of Tyrconnell

Oliver FitzWilliam, 1st Earl of Tyrconnell (died 11 April 1667) was an Irish nobleman.

His father was Thomas FitzWilliam, 1st Viscount FitzWilliam (1581-1650). His mother was Margaret Plunkett, daughter of Oliver Plunkett, 4th Baron Louth; through his mother he was related to the powerful Bagenal family. He was a younger son and did not expect to inherit the title or estates; like many young men in his position he read law, studying at Gray's Inn, and then resolved on a military career. With the help of James Butler, 1st Duke of Ormonde he became a Colonel in the French Army and showed both courage and military skill. On the death of his brother Richard he became heir to the title.

He was both a Catholic and a royalist, and enjoyed the confidence of Queen Henrietta Maria, who recommended him to Charles I as " a man deserving of every encouragement." In 1645 he tried to get the Confederation of Kilkenny to support King Charles I in the English Civil War on the grounds that their demands for full civic rights to be restored to Roman Catholics would be met. He fought with the Confederates against the Parliamentarians in 1645–6, and led a successful assault on Roscommon Castle in 1646. In 1649 he was imprisoned in London but soon released. After some time in France he was allowed to return to England through the pleas of his brother-in-law John Holles, 2nd Earl of Clare. He is said to have been one of the few Irishmen whom Oliver Cromwell admired, and was also on good terms with Henry Cromwell. During the Commonwealth he seems to have played a careful political game- his second marriage into the Holles family put him in the Parliamentarian camp, but he was also suspected of working for the Restoration of Charles II.

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