Bishop McGuckian grew up in Cloughmills, about 40 miles north of Belfast, as the youngest of six children. His father was a pig farmer. He has two brothers who are also Jesuit priests. He attended Queen's University in Belfast, studying Irish and scholastic philosophy, where he completed a master of arts in Irish translation. He attended schools in Dublin and Toronto, Canada, as well. After ordination as a Jesuit priest in 1984, he went on to teach, to work as a vocations director, and to spend time in spiritual renewal in Quezon City in the Philippines. He co-authored a drama, 1912 - A Hundred Years On, with a Presbyterian historian, Phillip Orr, which looked at the experiences of the Ulster Covenant and the wider Home Rule movement from both nationalist and unionist perspectives. He translated into Irish the autobiography of Ignatius of Loyola, the founder of the Jesuits. He served as chaplain to the Gaelscoilleanna and at Queen's University. He was appointed bishop of Raphoe (Donegal and Letterkenny areas) in 2017. In 2022 following a fatal explosion in Creeslough, County Donegal, that left 10 dead, Bishop McGuckian referred to it as the darkest day in Donegal. Bishop McGuckian concelebrated the funeral Masses for each of the victims. He has been bishop of Down and Connor since 2024.