Pope Francis has abolished the rule of "pontifical secrecy" as part of a number of changes to the way the Roman Catholic Church deals with cases of sexual abuse of minors.
It means priests will no longer be able to cite papal secrecy in abuse cases.
The Church has been rocked by thousands of reports of sexual abuse around the world by priests, and accusations of cover-ups by senior clergy.
The Pontiff's latest instructions regarding Vatican law on sexual abuse say that the pontifical secret no longer applies "to accusations, trials and decisions" involving such cases.
Marie Collins, a child sexual abuse survivor who in 2017 resigned from a Vatican committee she said was failing to adequately tackle paedophilia, welcomed the pope's latest move.
Excellent news. Recommended by PCPM during first term, so good to see it being implement. At last a real and positive change. https://t.co/8ZKm2TKRR7— Marie Collins (@marielco) December 17, 2019
Reacting to the news, Executive Director of the group One in Four Maeve Lewis welcomed the decision but said that they were worried it would only apply in countries where there is legislation to that affect and in many developing countries it is not an obligation to inform authorities.
She said many of their clients had been put under a vow of secrecy in the past when they did notify the Catholic authorities.
Abuse survivor and campaigner Colm O'Gorman described it as a step forward.
He said it was finally an admission of something that many have been saying went on for decades.
He said that this needs to be about responding to historic abuses but also preventing future abuses. He said that child safety should be paramount.
Pontifical secrecy is a rule of confidentiality designed to protect sensitive information related to Church governance, such as diplomatic correspondence, personnel issues and alleged crimes.
Critics say the secrecy laws have prevented priests and victims from reporting abuse, as well as hindered national justice systems prosecuting cases.
The Vatican also announced today that it was raising the age at which sexual images of a person were deemed child pornography from 14 to 18.
In May, the pope passed a landmark measure to oblige those who know about sex abuse to report it to their superiors, a move expected to bring even more cases to light.
In a statement, issued on the Argentine pontiff's 83rd birthday, the Pope laid out the new obligations.
"The person who files the report, the person who alleges to have been harmed and the witnesses shall not be bound by any obligation of silence with regard to matters involving the case," he wrote.
Archbishop of Malta Charles Scicluna, the Vatican's chief sex crime investigator, called the move an "epochal decision that removes obstacles and impediments."
He told the official Vatican News website that "the question of transparency now is being implemented at the highest level."
The Pope has vowed an "all-out battle" against sex abuse within the Church, but some victims' groups have said concrete measures have been slow in coming.
Despite the lifting of papal secrecy, Pope Francis qualified that discretion in sexual abuse cases was still required.
Information pertaining to such cases should be treated, "in such a way as to ensure its security, integrity and discretion... for the sake of protecting the good name, image and privacy of all persons involved," the Pope wrote.
But that should not obstruct the law, the obligation to report abuses and the carrying out of requests by law enforcement, the instructions said.