In an unprecedented move personally sanctioned by Pope Francis, Polish cleric Jozef Wesolowski was placed under house arrest in the Vatican on Wednesday pending the outcome of criminal proceedings launched by the city state's authorities.
Wesolowski, 65, was defrocked in June after a church tribunal found that he had abused minors during his 2008-2013 stint as the Vatican's ambassador to the Dominican Republic.
He was living in a covent in Rome until the arrest, La Repubblica reported.
If the secular criminal proceedings against him result in a trial it will be the first for sex abuse to take place within the walls of the Holy See.
"There will probably be a trial," Vatican spokesman Federico Lombardi told AFP on Wednesday.
He declined to offer an estimate of when it might take place but stressed that legal action against Vatican officials has a recent precedent in the case of Paolo Gabriele, the former butler to now-retired Benedict XVI who was convicted in October 2012 of stealing papal documents in what was known as the Vatileaks scandal.
Gabriele was detained under house arrest prior to the trial and for two months after it before being released under a papal pardon issued by Benedict just before Christmas 2012.
Critics of that trial suggested the Vatican had stage-managed it to produce a verdict which conveniently suggested that Gabriele acted alone, thereby stifling any further revelations about corruption, nepotism and bitter infighting.
In the Wesolowski case, the Vatican had come under fire for withdrawing him to Rome when the allegations first surfaced and for subsequently declining to go along with an extradition request from the Dominican authorities. Extradition moves by Wesolowski's native Poland were also rebuffed.
Earlier this year, the UN children's rights watchdog cited the lack of action over Wesolowski in a damning indictment of the Catholic Church failure to address the issue of clerical paedophilia that has become a global issue in recent years.
Lombardi insisted that the decision to take action against the former archbishop was a sign of how seriously the Vatican and Francis took the issue.
"This is the result of the Pope's express wish for a case this serious and sensitive to be dealt with without delay, with the necessary scrupulousness and full undertaking of responsibility on the part of the institutions which head up the Holy See," Lombardi said.
Francesco Clementi, an expert in the complex legal and constitutional structures surrounding the micro-state, also interpreted the move as a sign the Vatican was facing up to its responsibilities to the victims of abuse.
"It is a very strong and powerful change of direction that is also highly symbolic," he told La Stampa.
"Francis has made a clear choice: in the state where he is sovereign and pontiff there is no place for clergy or lay people suspected of sexual abuse, particularly of minors."
Wesolowski was ordained in 1972 by the then-archbishop of Krakow, Cardinal Karol Wojtyla, who later became Pope John Paul II and was elevated to sainthood this year.
In his time at the Vatican, John Paul named Wesolowski as envoy to Bolivia and he also served in several Asian countries before his stint in the Dominican Republic.
Francis has promised a crackdown on paedophile priests. Last year, he overhauled Vatican law in the area with a special decree declaring that sexual violence and sexual acts with children, child prostitution and child pornography were punishable by up to 12 years in prison.
In May he warned there were "no privileges" for bishops when it came to child sex crimes and likened sexual abuse to a "Satanic Mass".
Church prosectors have dealt with nearly 3,500 abuse cases in the last decade, defrocking 848 and ordering more than 2,500 to live a life of prayer and penance.