Plunkett, Patrick (1603–79), catholic bishop and confederate, was the second son of Christopher Plunkett, 9th Lord Killeen, and Jane, daughter of Sir Lucas Dillon (qv). Plunkett's elder brother, Luke, became 10th Lord Killeen and earl of Fingall, while his younger brother, Nicholas (qv), a barrister, rose to political prominence within the Catholic Confederate Association. After his early education Patrick entered the Cistercian order, probably abroad, and was eventually made titular abbot of the then dissolved St Mary's abbey, near Dublin, and parish priest of Kilcloon. There he tutored his young cousin, Oliver Plunkett (qv), from infancy to manhood. Familial connections facilitated his acquisition of the ancient site of St Mary's, where in 1641 he built an oratory and house for six of his community. However, they were expelled during the outbreak of unrest that October. Active among the catholic confederates, largely due to the influence of his brother Nicholas, he attended the clerical synod at Waterford in August 1646, where he opposed the first Ormond peace. Later that year he was among those clerics who governed in association with the confederate supreme council.
At the council's behest the papal nuncio, GianBattista Rinuccini (qv), recommended Plunkett to the see of Ardagh, and he was consecrated bishop at Waterford in March 1648, despite the protests of native clergy, who favoured the appointment of a diocesan. In this capacity Plunkett ordained 250 priests. His name does not appear on the condemnation of the Inchiquin truce in May 1648 and he was among those moderate bishops who wrote to Rinuccini urging him to come to an accommodation with the supreme council that June. He incurred the nuncio's disfavour when he defied his summons to a proposed clerical synod in July 1648. As the confederates split over the terms of a peace settlement, Plunkett distanced himself from the nuncio's position, supporting the second Ormond peace. He was one of nine bishops who on 18 January 1649 encouraged their congregations to observe its terms. During 1649 he continued to adopt a moderate stance and was absent from the Jamestown synod which condemned the actions of James Butler, marquess of Ormond (qv), in August 1650. He attended the assembly at Loughrea in November 1650, but with the intensification of the Cromwellian persecution fled to the Continent. While in Europe he was involved in attempts to secure a general absolution from Rinuccini's censures, incurring the disfavour of Masari, secretary to the Sacra Congregatio de Propaganda Fide. He wrote to Edward Nicholas, secretary of state, from Normandy in December 1662 about attempts to secure his support for a loyal catholic remonstrance.
On the understanding that he was supportive of this, Plunkett was allowed return to Ireland in late 1664 or early 1665 and on arrival took up residence with his brother in Dublin. He was now the only bishop in Ireland exercising his ecclesiastical duties. To the surprise of the authorities, he led the opposition to the loyal remonstrance in 1666 and was imprisoned, though family connections ensured his speedy release. He was appointed bishop of Meath in January 1669, and attended the synod of Irish bishops in Dublin in June 1670 and the provincial synod in Clones that August. Oliver Plunkett consistently commended his relative's diocesan administration, and defended him against allegations of non-residence and neglect. He attended the provincial synod of Ardpatrick in August 1678, but later that year requested a co-adjutor because of his failing health. He died 18 November 1679 and was buried in the family plot at Killeen.