 In 1815 he was appointed Prefect and Professor of the Dunboyne Establishment at Maynooth College.In 1843 McNally was appointed the Coadjutor Bishop of the Diocese of Clogher in Ireland succeeding less than a year later on 20 February 1844, following the death of his predecessor Bishop Edward Kernan.The esteemed Irish ecclesiastical historian Donal Kerr assessed McNally as an "O'Connellite Bishop and Reforming Pastor", the son of a 'middling farmer' who grew up in the aftermath of the 1798 Rising and would live long enough to see the stirrings of the Fenian Rising.