[2] Born in Dublin, County Dublin, Ireland, in 1930, McDermott studied for the priesthood first with the Dominicans, then at St. Patrick's, Carlow College, completing his studies he was ordained a priest on 5 June 1955 for the Diocese of Birmingham in Alabama, United States.
For fourteen years, he led a rural parish in Huancarama in the Apurímac Region, where he learned the Quechua language.
He knew govern his diocese in very difficult times for material and spiritual poverty and terrorism.
In January 2005, Bishop Demetrio Molloy suffered a triple stroke which left him paralyzed until his death.
Each week, the priests of his diocese eleven hours traveling to Lima to accompany and pray with their bishop who was under the care of the Daughters of St. Camillus Nursing Home in the Tezza Clinic, where offered all his sufferings by the good of the Church.