MacGillapatrick, Brian (c.1500–75), was the son of Brian MacGillapatrick, lord of North Ossory, and probably Honora O'More. It is unknown when exactly Brian succeeded his father as lord of North Ossory, but at first he tried to maintain his family's attachment to Gerald Fitzgerald (qv) (d. 1534), 9th earl of Kildare. This changed dramatically during late 1532. The chain of events that led to Brian's desertion of the Kildare cause began with a raid upon the lands of the Butlers by his brother Diarmait MacGillapatrick of Ballykeely. As Diarmait and his men made off with their prizes to the safety of North Ossory, Thomas Butler led a posse in pursuit. In the confrontation that followed, Diarmait's men killed Butler, angering his father, Piers Butler (qv) (d. 1539), earl of Ossory (later earl of Ormond). Ossory was bent on revenge, and Brian handed Diarmait over to him for punishment. Capping this performance was Brian's taking of Ossory's daughter Margaret Butler (d. c.1546) as his second wife. By this stage Brian's first wife, Joan O'Carroll, was probably dead.
The MacGillapatrick realignment and the civil war among the O'Carrolls of nearby Ely was to turn the midland war in favour of the Butlers and to the detriment of Kildare. At Waterford in September 1533 Brian gave a detailed statement about the killing of Thomas Butler, implicating Kildare in the murder. This disposition proved invaluable to Henry VIII's chief minister, Thomas Cromwell (d. 1540), who was about to question Kildare about his mismanagement of Irish affairs. In the aftermath of the rebellion of Thomas FitzGerald (qv) (d. 1537), 10th earl of Kildare, Brian MacGillapatrick emerged as a winner. But Brian's ever-strengthening position received unwelcome attention in June and July 1536 from Conall O'More (qv) of Laois (d. c.1537), forcing Lord Deputy Leonard Grey (qv) to intervene to stop their conflict. Despite this, Ossory remained the only noble in Ireland able to control the Irish of the midlands. Testifying to this state of play was the presence of Conall O'More of Laois and Ossory as surety to the submission on 14 July of Cathaoir MacMurrough (qv) (d. c.1544), and the earl's role in the negotiations with Brian to end his feud with O'More.
The new Tudor government, however, was determined not to allow Ossory to gain the dominant position formerly enjoyed by Kildare. As part of this policy Grey concluded an indenture with the lord of North Ossory on 8 November 1537. This agreement had the effect of detaching the MacGillapatricks from the Butler party by granting them government protection. This was to bolster the government's position in the midlands, and Grey formally recognised the territorial integrity of the MacGillapatrick lordship and, importantly, declared it not to be part of the Butler-dominated Co. Kilkenny. Furthermore Grey extended Brian the protection of English law. Yet Brian chose his actions and words carefully to maintain his relative independence, steering his dynasty through the political minefield that was the increasingly bitter struggle between Grey and the Butlers. Crucial to this double-edged strategy was his appreciation of the military power of the Butlers and their influence at the English court. Their pervasive influence was to bring Grey's lord deputyship crashing down in 1540, and culminated in his execution in 1541.
In spite of this Brian was to have further successes with Grey's successor, Lord Deputy Sir Anthony St Leger (qv). St Leger endeavoured to keep Brian in the government camp. During early 1541 Brian surrendered his lordship to St Leger as part of the government programme of ‘surrender and regrant’. By its terms he agreed to adopt English language, custom and dress and was to answer to the courts of common law. Thus, in June 1541, MacGillapatrick, through St Leger's patronage, was granted the title of baron of Upper Ossory. This allowed him to take his place among his fellow barons in the Irish house of lords at the opening sessions of the 1541 parliament. Even though Brian apparently hovered around the camp of the lord deputy, his policy – as ever – was dominated by self-interest, and he pressed his rights to territories in the north of Co. Kilkenny in 1543.
However, he cannot have been pleased that the struggle between James Butler (qv) (d. 1546), 9th earl of Ormond, and St Leger had become concentrated in the dynastic struggles dominating the nearby O'More and O'Connor Faly lordships of Laois and Offaly. To protect himself, Rory Caoch O'More (qv) (d. 1547) moved closer to Ormond, marrying Margaret Butler (d. 1601) in 1543/4. This alliance so alarmed Brian in 1544 that he now allied himself with Brian O'Connor Faly (qv) (d. c.1560) to prevent encirclement by Ormond and his clients. St Leger and O'Connor Faly then encouraged Brian to exploit Rory Caoch's struggle with his brother Giollapadraig O'More (d. 1549), attacking Laois. This resulted in Brian's brief imprisonment in Dublin on the orders of Ormond's friends in the government. Brian now realised that he needed to be more ambivalent in his dealings with St Leger, and it is clear he learned from this experience, playing both sides to his advantage between late 1544 and 1545.
With the encouragement of his third wife, Elizabeth O'Connor Faly (daughter of O'Connor Faly, and former wife of Giollapadraig O'More), Brian was to grow cooler in his dealings with the government during the late 1540s and early 1550s. This policy has more to do with Brian's finely honed survival instincts than any genuine sympathy for the O'Mores and O'Connor Falys in their resisting the plantation of their lordships. During the late 1540s Brian's ‘friendly’ policy towards the O'Mores and O'Connor Falys ensured that they would not raid his lordship, freeing him to fight the expansionist Viscount Richard Butler (qv) of Mountgarret (d. 1571) to a standstill in 1552.
With the return in 1554 of Brian's famously English-educated son, Barnaby Fitzpatrick (qv) (d. 1581), from England, the political equilibrium in North Ossory slowly began to shift. With the support of the government, and a sizeable contingent of his kinsmen who hated Elizabeth O'Connor Faly, Barnaby slowly eroded the position of the now ageing Brian. Sometime after 17 August 1559 Barnaby made his move and deposed his father surprisingly easily, making Brian his prisoner. Although Brian, from his confinement, continued to plot against Barnaby, his power was broken. In 1566 Barnaby declared his father mentally incapable and petitioned the queen for a grant of his estate. Two years later Elizabeth granted Barnaby Upper Ossory, even though Brian still lived. However, Barnaby was not to become the 2nd baron of Upper Ossory until the death of his once formidable father in 1575.