Niall Coll was born in 1963, the eldest of four children, to Willie and Kathleen Coll, St Johnston, Co. Donegal.

Niall attended St Baithin’s NS, St Johnston and St Eunan’s College, Letterkenny. In September 1981 he entered the National Seminary at Maynooth to begin his formation for the priesthood. He obtained a Bachelor of Arts Degree in History and Geography in 1984 and a Bachelor in Divinity in 1987. He was ordained to the priesthood by Bishop Seamus Hegarty for the Diocese of Raphoe in 1988. Following a two-year period of post-graduate study in Rome he was conferred with a Licence in Theology by the Gregorian University.

Having completed his studies Father Niall was appointed to St Eunan’s College, Letterkenny in 1989, as chaplain and teacher. Three years later he obtained a Higher Diploma in Education from Trinity College, Dublin. In 1992 he was sent to Rome to study for a Doctorate in Theology at the Gregorian University. In 1995 he was awarded a Doctoral Degree for a thesis in Christology which was later published as Christ in Eternity and Time: Contemporary Anglican Perspectives (Dublin: Four Courts Press, 2001). 

Following his return from Rome in 1995 he was appointed as a lecturer in Systematic Theology in St Patrick’s College, Carlow. Three years later he returned to Raphoe Diocese as both chaplain in Pobalscoil na Rossan and curate in the parish of Dungloe. In 2001 he was appointed as Senior Lecturer in Religious Studies and Religious Education at St Mary’s University College, Belfast (a college of Queen’s University, Belfast).

In 2020, at the height of the Covid 19 pandemic, he returned to the Raphoe Diocese as parish priest of Drumholm (Ballintra and Laghey) and a year later was transferred to the neighbouring parish of Tawnawilly (Donegal Town and Clar).

Bishop Niall is editor (with Paschal Scallon CM) of A Church with a Future: Challenges to Irish Catholicism Today (Dublin: Columba Press, 2005) and also of Ireland and Vatican II: Essays Theological, Pastoral and Educational (Dublin: Columba Press, 2015). He was for many years editor of Le Chéile: A Catholic Schools Ethos Journal published by St Mary’s University College which sought to promote the values and work of Catholic education locally. He is a member of the Irish Inter-Church Committee. 

His appointment as Bishop of Ossory by Pope Francis was announced on October 28th, 2022. Bishop Niall was ordained as the 96th Bishop of Ossory on 22nd January 2023 by Archbishop Dermot Farrell, who himself had served as Bishop of Ossory.