O'Loughlin began his career as a teacher in the University College Dublin, and was later made a scholar at the School of Celtic Studies in the Dublin Institute for Advanced Studies. In 1997, he worked in the Department of Theology and Religious Studies in the University of Wales, Lampeter, where he became the first Professor of Historical Theology in the University of Wales in February 2006. He joined the University of Nottingham in 2009.
- Teachers and Code-Breakers: The Latin Genesis Tradition, 430-800 [Instrumenta Patristica XXXV] (Brepols, Turnhout, 1999).
- Saint Patrick: The Man and his Works (S.P.C.K., London 1999).
- Celtic Theology: Humanity, World and God in Early Irish Writings (Continuum [Cassell], London 2000).
- Journeys on the Edges (D.L.T., London / Orbis, New York, 2000).
- Liturgical Resources for Lent and Eastertide (Columba Press, Dublin 2004).
- Discovering Saint Patrick (D.L.T., London / Paulist Press, New York/Mahwah, N.J., 2005).
- Liturgical Resources for Advent and Christmastide (Columba Press, Dublin 2006).
- Liturgical Resources for the Year of Luke (Columba Press, Dublin 2006).
- Adomnán and the Holy Places: The Perceptions of an Insular Monk on the Location of the Biblical Drama (T. & T. Clark, London 2007).
- Liturgical Resources for the Year of Matthew (Columba Press, Dublin 2007).
- Explaining the Lectionary for Readers (Columba Press, Dublin 2008).
- Liturgical Resources for the Year of Mark (Columba Press, Dublin 2008).