Archbishop Diarmuid Martin, the Holy See's Permanent Observer at the UN in Geneva, has been formally appointed coadjutor Archbishop of Dublin.
Pope John Paul II made the announcement in a statement this morning.
Dr Martin, (58) is the Titular Archbishop of Glendalough, Apostolic Nuncio and Permanent Observer of the Holy See at the Office of the United Nations in Geneva.
He will succeed Cardinal Desmond Connell (77) on his retirement.
Speaking after a Mass at the Dublin Pro-Cathedral this morning, Dr Martin promised to help victims of the sex abuse scandal that has rocked the Catholic Church.
"I am aware that there are those for whom meaning and hope were lost in their lives through the actions of church personnel.
"Their hurt is all the greater if they feel betrayed by someone they turned to in trust."
The Primate of All-Ireland and Archbishop of Armagh, Most Rev. Seán Brady said Dr Martin "will work most generously and untiringly in the best interests of the people entrusted to his care".
The Taoiseach, Mr Ahern, welcomed the ordination, describing Dr Martin as a "pastor of international reputation."
"In his work in pursuit of justice and peace he has been a notable and respected voice in the international arena," Mr Ahern said. "His evident concern for a just international order and for the needs of the poor and oppressed has lent authority to that voice."
Fr Martin Cosgrove, chairman of the Twelfth Council of Priests of Dublin, said the Archbishop is "a distinguished native son and Priest of the Diocese who has served the Universal Church with great distinction".