Born in St. John's, Newfoundland, Dunn was raised in the mining community of Buchans where he attended primary and elementary school before moving to the fishing community of Harbour Grace where he attended secondary school. Dunn attended Memorial University of Newfoundland for one year before transferring to King's University College of the University of Western Ontario where he graduated with a B.A. in 1976. Dunn completed seminary formation at St. Peter's Seminary, graduating with a M.Div. in 1979. Dunn undertook post-graduate studies and graduated with a J.C.L. and J.C.D. from St. Paul University in 1990 and 1991 respectively. He completed a M.Th. at University of Notre Dame in 2006.
Priest
Dunn was ordained a priest in the Diocese of Grand Falls on 28 August 1980, where he served as a Parochial Vicar at the Cathedral of the Immaculate Conception in Grand Falls-Windsor from 1980 to 1985. Dunn then served as Pastor of St. Gabriel's Parish in St. Brendan's from 1985 to 1988, and then as Pastor of the Cathedral of the Immaculate Conception in Grand Falls from 1991 to 1996. He was subsequently Pastor of St. Joseph's Parish in Harbour Breton from 1996 to 1999, followed by the position of Pastor for both Holy Cross Parish in Holyrood and St. Peter and St. Paul Parish in Harbour Main from 1999 to 2002. Dunn served the Diocese of Grand Falls as Vice-Chancellor, Chancellor, Member of the College of Consultors, Bishop's Canonical Advisor, Judge for the Marriage Tribunal, and Associate Judicial Vicar of the MarriageTribunal. Dunn has also served a lecturer with the Atlantic School of Theology for the Diploma Program for Theology and Ministry, lecturer in the Faculty of Canon Law at St. Paul University, and served on the faculty at St. Peter's Seminary where he taught courses in Canon Law, Ecumenism, Ecclesiology, and Liturgical Law; he served as Dean of Studies from 2005 to 2008.
Bishop
In 16 July 2008, Pope Benedict XVI named Dunn auxiliary bishop of the Diocese of Sault Sainte Marie. He received his episcopal consecration from Bishop Jean-Louis Plouffe at Cathedral of the Immaculate Conception in Grand Falls, Newfoundland and Labrador on 9 October. On 21 November 2009, Pope Benedict appointed Dunn Bishop of Antigonish. Dunn was installed on 25 January 2010. He replaced Raymond Lahey, who was facing charges of possessing and importing child pornography. He became ex officio Chancellor of St. Francis Xavier University as well. Dunn was elected by the to participate in the 13th Ordinary General Assembly of the Synod of Bishops on the New Evangelization in October 2012. He spoke on methods of evangelizing victims of clerical sexual abuse. He proposed "the appointment of pastoral teams consisting of clergy and laity, an official reflection on and recognition of lay ecclesial ministers, a deliberate and systematic involvement and leadership of women at all levels of Church life, e.g., permitting women to be instituted as lectors and acolytes and the institution of the ministry of catechist". On 13 April 2019, Pope Francis named Dunn Archbishop Coadjutor of Halifax-Yarmouth.
