The archbishop, a longtime member of the Vatican diplomatic corps and former Vatican Secretariat of State expert on Southeast Asia, has been nuncio to Guatemala since 2009.
In his first posting as a nuncio, Blessed John Paul II sent him to Burundi in 2004 to replace Archbishop Michael A. Courtney, who was gunned down by unknown assailants as he was traveling in a car a month earlier.
The nuncio's death in Burundi marked the first time in the modern age that a papal ambassador had been assassinated.
In an interview with Catholic News Service in 2000, then-Msgr. Gallagher said though an ambassador's life is filled with protocol, social niceties and cocktail parties, the Vatican foreign service counts less on "social animals" than on good priests.
The Holy See looks for "someone who can express his priesthood through his diplomatic work," said the Liverpool-born cleric, who served as the Vatican permanent observer at the Council of Europe from 2000 to 2004.
Ordained to the priesthood in 1977, he later earned a degree in canon law and studied at the Pontifical Ecclesiastical Academy, which trains Vatican diplomats.
He joined the Vatican's diplomatic service in 1984, serving in nunciatures in Tanzania, Uruguay and the Philippines.
He worked at the Vatican Secretariat of State from 1994 to 2000.