Career
O’Reilly was appointed the Coadjutor Bishop of the Diocese of Clogher in Ireland on 27 April 1777. He was ordained a bishop on 29 July of that same year. He became Roman Catholic Bishop of Clogher on 28 March 1778, following the death of his predecessor, Daniel O'Reilly.
Ordained a bishop at the age of thirty eight years, Hugh O’Reilly was the youngest bishop of the diocese in modern times. He died in office in on 3 September 1801 having served as bishop of his diocese for almost twenty-four years. O’Reilly was succeeded by Bishop James Murphy, who had was appointed his Coadjutor Bishop in May 1798.