A Dominican friar, he was elected Archbishop of Armagh by the Sacred Congregation for the Propagation of the Faith on 14 December 1683. By a papal brief, dated 12 January 1684, he was empowered to perform archiepiscopal functions without the Pallium. During the revolution of 1688, Maguire and other Catholic prelates were instrumental in saving from destruction the valuable library of Trinity College, Dublin. In 1691, he fled to France, and took refuge in Paris from his persecutors.