Abbot Brendan was born in Ennis, Co Clare in 1970. After studies in Maynooth and Rome, he was ordained a priest of the Diocese of Killaloe in 1995. After ordination, he pursued postgraduate studies in canon law at the Gregorian University in Rome, after which he was appointed curate in the parish of Kilrush. He entered Glenstal Abbey in 1998, taking the name Brendan. He professed his simple vows in 1999 and made his solemn profession in 2002.
After some years working in the abbey school as a housemaster and teacher of classics, Father Coffey spent two years in Padua in Italy completing postgraduate studies in liturgy. On his return to Glenstal, he served as Prior of the monastery from 2007 until 2015. He spent the academic year 2015-16 at the Catholic University of America completing doctoral studies in liturgy.