Hackett, John Baptist (c.1606–1676), Dominican priest and theologian, was born into a very prominent Norman-Irish family at Fethard, Co. Tipperary. He entered the Dominican order and made his profession at Cashel; he then studied in Spain and was ordained deacon and priest at Barcelona in 1630. He lectured with distinction at the order's colleges at Milan, Naples, and Rome, and at the meeting of the Dominican general chapter in 1644 received the order's most highly prized theological degree, the mastership in sacred theology. His reputation made him eagerly sought as a theological adviser by several Roman cardinals, including Aemilius Altieri; when Altieri became Pope Clement X, he appointed Hackett his personal theologian. Hackett was offered several Italian bishoprics and the cardinalate but refused them.
Hackett was regent of studies at Sant'Eustorgio, Milan, where he decisively influenced Lord Philip Howard (1629–94), son of the protestant duke of Norfolk, in his decision to join the Dominican order at Cremona in 1645. The Howard family's attempts to prevent Lord Philip from becoming a Dominican or taking holy orders eventually led to the involvement of the pope, who tested and approved Howard's vocation and his intention to work for the restoration of the catholic faith in England. Howard entered Santa Maria alla Sanità in Naples, the house of formation for English, Irish, and Scottish Dominicans intending to join the priesthood, and on 29 May 1675, in a move promoted by Hackett, he was named a cardinal by Clement X.
Hackett continued to be active as a theologian and in his later years published in Rome a number of works on Thomist theology and philosophy. They included Controversorium theologicum complectens omnes tractatus totius primate secundae Doctoris Angelici D. Thomae Aquinatis (1654); Synopsis theologica in tractatum de fide, spe et charitas (1659); Synopsis summulistica (1659); Synopsis physica (1659); Synopsis meteorica (1659); Synopsis philosophiae, (2 vols, 1662); Synopsis universa theologiae scholasticae et moralis in quinque tomos distributa iuxta mentem Doctoris Angelici D. Thomae Aquinatis (1663). He died 26 August 1676 at the Dominican convent of Santa Maria sopra Minerva, Rome, and was buried in its basilica.
Two of Hackett's kinsmen from Cashel also became Dominicans. Pádraigín Haicéad (qv) spent most of his life in exile, but became one of the finest Irish-language poets of the seventeenth century. Patrick Kearney graduated from the University of Louvain in 1637, was subsequently appointed a professor and master of theology (1650) in the Irish Dominican college of Louvain.