 Agar served as Dean of Kilmore (1765–1768) and Bishop of Cloyne (1768–1779).In 1779 he was admitted to the Irish Privy Council and appointed Archbishop of Cashel, which was an archbishopric until 1838, an office he held until 1801, and was then Archbishop of Dublin from 1801 to 1809.Agar is known to have held particularly marked Calvinistic positions.