A member of the Ó hÍceadha bardic family, he received his early education in his native place, entered the college of St. Antony at Leuven (French: Louvain), which had just been founded for Irish Catholic students, and received the Franciscan habit on 1 November 1607. Among his teachers at Leuven were the Irish scholars Hugh Mac an Bhaird (Ward) and Hugh Mac Caghwell, later Roman Catholic Archbishop of Armagh.
After his ordination to the priesthood, Hickey was appointed lecturer in theology at Leuven, and subsequently professor in the college of St. Francis at Cologne. In 1619 he was summoned to Rome to collaborate with Luke Wadding in preparing for publication the Annals of the Franciscan Order, and the works of Duns Scotus.
He took an active part in the labours of the commissions appointed by Pope Urban VIII to revise the Roman Breviary, and to examine into the affairs of the Eastern Church. At the general chapter of the order held in Rome in 1639, he was elected definitor general.
He lived for some time at S. Pietro in Montorio on the Janiculum and, from 1624 till his death, in the college of St. Isidore.
During the discussions which were held in Rome concerning the doctrine of the Immaculate Conception, Hickey won distinction by his learning and acuteness. His treatise on this subject is called by Marracius (Bibliotheca Mariana) "opus insigne et absolutum". In his work on the Fourth Book of Sentences, he shows great breadth of view and critical perception; in addition to the scholastic method, he makes use of the historical method and fully recognizes the development of sacramental theology.
- "Commentarii in Lib. IV Sententiarum" (Lyons, 1639)
- "Nitela Franciscanæ Religionis" (Lyons, 1627); in this book he refutes defends the early history of the Franciscan Order against Abraham Bzovius;
- "De Conceptione Immaculata B. Mariæ Virginis";
- "De Stigmatibus S. Catharinæ Senensis", written by order of the Sacred Congregation of Rites;
- "Ad pleraque dubia moralia, et ascetica, gravissimæ responsiones". This work, which Wadding calls "opus doctissimum", is still in manuscript.
Among the manuscripts preserved in the Franciscan Convent, Dublin, were several letters written to Father Hickey from Ireland on the civil and ecclesiastical affairs of that country. There is also an important letter of his on the Irish language. Many of the Irish bishops consulted him on matters of grave moment. His acquaintance with the history, language, and antiquities of Ireland was extensive, and in co-operation with John Colgan, Hugh Ward, and other Irish scholars, he drew up a plan for a critical history of Ireland in all its branches, — but this idea was not realized.
- Wadding-Sbaralea, Scriptores Ord. S. Francisci (Rome, 1806);
- Joannes a Sancto Antonio, Bibliotheca Universa Franciscana (Madrid, 1732);
- Nicolas de Vernulz, Academia Lovaniensis (1667);
- Ware-Harris, Works (Dublin, 1764);
- Michael John Brenan, Ecclesiastical History of Ireland (Dublin, 1840).