O'Hartegan, Matthew (1600–66), Jesuit priest and confederate agent, was born in August 1600 in Limerick. Originally intending to pursue a lay career, he studied philosophy and jurisprudence, and was awarded an MA, but subsequently entered the Society of Jesus at Bordeaux on 8 January 1626. After a short period of regency at Agen, he began theological studies at Bordeaux in 1630. He was ordained in spring 1633, and thereafter became professor of philosophy at Pau. He was transferred as minister to the college of La Rochelle in 1636, and at the end of that year was assigned to the Irish mission. There are no records of his term in Ireland, except that he made his solemn profession at Waterford, on 15 August 1641. He acted on behalf of the Catholic Confederate Association in Paris in 1642, and he and Geoffrey Barron (qv) were officially appointed agents to the French court by the supreme council on 23 July 1643. His efforts to ensure the continued support of France and to procure aid involved him in contact with the papal nuncio in France, Grimaldi, Cardinal Mazarin, and Charles I's queen, Henrietta Maria.
In March 1645 the confederate supreme council expressed concern at a number of letters allegedly written by O'Hartegan, which criticised the influence on the council of Charles I's viceroy, James Butler (qv), marquess of Ormond. Although the council stated that it believed the letters to be forged, O'Hartegan's suitability to act for the association was increasingly called into question, with concerns over his ‘vanitye, and exaltation of himselfe’ and ‘disrespect and scandalous calumnyes by him’ (Gilbert, Ir. confed., iv, 205). He also alienated Henrietta Maria, who doubted the sincerity of his desire for peace.
In regular contact with GianBattista Rinuccini (qv) in Paris, he organised the nuncio's passage to Ireland. Rinuccini discussed the possibility of O'Hartegan's returning to his religious duties in October 1645; he ultimately finished or resigned his agency in Paris in May 1646 and returned to Bordeaux. Despite this, he retained an interest in developments in Ireland, and continued to voice his suspicions about the integrity of royal intentions. The general of the Society of Jesus, Father Caraffa, made a request to the provincial at Bordeaux 1648 to choose a priest for an examination of the Irish mission. O'Hartegan was deeply involved in this process, and the ultimate choice, Mercure Verdier, owed much of his familiarity with the complex politico-religious situation in Ireland to O'Hartegan. However, O'Hartegan was never again recalled to the Irish mission. He held a number of posts in his own province of Aquitaine, including professor of philosophy at Bordeaux (1646–8), and at Pau (1648–50). In the mid 1650s the general of the society expressed concern about the spiritual welfare of Irish inhabitants on the island of St Kitts, prompting O'Hartegan's offer to settle there; however, he does not appear to have gone to the West Indies. He held the professorship of philosophy at Agen 1657–60 and also conducted much weighty business for his province at Paris, briefly acting as superior at Bayonne. In 1660 he was assigned to the Grand College of Poitiers where he served as operarius until his death on 2 May 1666.