It is understood the Emeritus Bishop of Down and Connor passed away this morning.
The EU's Apostolic Nunciature is an ecclesiastical office of the Catholic Church with offices in Brussels.
Pope Francis announced the appointment of Archbishop Treanor to the role in 2022.
Archbishop Treanor was born on Christmas Day in 1950 in Monaghan town.
He completed his early education at Saint Mary’s Christian Brothers School in Co Monaghan.
He pursued his third level education at Saint Patrick’s College, Maynooth and in Rome.
He was ordained a priest in 1976 for service in the diocese of Clogher in Saint Macartan’s Cathedral, Co Monaghan.
He was appointed to the staff of the Commission of the Bishops’ Conferences of the European Union (COMECE) in 1989.
Archbishop Treanor was appointed Secretary General of COMECE four years later.
A post he continued to hold until his appointment by Pope Benedict XVI as Bishop of Down and Connor in 2008.
He began working in the role of the Apostolic Nuncio to the European Union in January 2023.
Archbishop Treanor is survived by his brother John and his sister Mary.