Studies on Irish architectural history following the Act of Union in 1801 have concentrated on public buildings. This article introduces an important new perspective to the subject by exploring John Nash (1752–1835) and his work in Ireland from 1803 to 1810. Nash is best known for the work he undertook for the prince regent, later King George IV. Relatively little is known of his other clients. However, patronage connections were singularly important to Nash and it was ultimately their high social and political profile that contributed to his career's upward trajectory. Nowhere are these connections more evident than in Ireland, where practically all of Nash's clients can be linked to his first known Irish patron, James Stewart (1741–1821) of Killymoon Castle in County Tyrone, and his wife Elizabeth née Molesworth (1751–1835). The timing of Nash's arrival in Ireland within a year of the Act of Union is also significant. Many of his Irish clients were new MPs at Westminster or representative peers elected to the House of Lords whose shared desire for personal aggrandisement found form in building works. In spite of Nash's often troubled relationships with his clients, his architectural output in Ireland was versatile and involved a variety of styles. As Nash's involvement with the prince regent grew, his supervisory role in Ireland passed to his pupils James and George Richard Pain, who in time established successful architectural practices of their own in the country. Few of Nash's Irish buildings have survived the test of time, but his legacy in Ireland is preserved in the works of the Pain brothers, whose design style remained remarkably faithful to their teaching master.