A joint statement on Tuesday said the process of digitising the archives had been completed and that procedures to access the information would be forthcoming.
No date was set, and the opening for now is restricted to victims, detainees, their relatives and the religious superiors of victims who were priests or nuns.
Official estimates say about 13,000 people were killed or disappeared in a government-sponsored crackdown on leftist dissidents during Argentina’s 1976-1983 “dirty war.”
Human rights activists believe the real number was as high as 30,000.
The statement said the decision to open the Church’s archives was taken at the express direction of Pope Francis, “in the service of truth, justice and peace.”
Francis — then Fr Jorge Mario Bergoglio — was the young Jesuit superior in Argentina during the military dictatorship, making his decision to open the archives all the more remarkable.
Many senior clerics were close to Argentina’s military rulers at the time and human rights groups have accused them of complicity with the regime.
Several books published since Pope Francis’s election as pontiff have asserted that his public silence actually enabled him to save more lives, using back channels to create a logistical network to save those who had been targeted for elimination by the military.
He had pledged to open the archives when pressed by relatives of Argentina’s “desaparecidos” or disappeared, particularly the Mothers of the Plaza de Mayo, mothers of the disappeared.
The documents concern archives held in the Vatican secretariat of state, the Vatican’s Buenos Aires embassy and the Argentine bishops’ conference.
Most would normally never be made public, and in the case of the Vatican archives, they would only become available to academics starting around 2075.
The Vatican spokesman, Greg Burke, stressed that for now the archives would only be open to victims and their relatives, not academics. He suggested that a broader opening could come later.
Activists say the Church has yet to fully apologise for its human rights record, identify those responsible for the many violations the Church knew about at the time, or lead Argentina’s justice system to bodies and to people who were stolen as babies from their birth families.
Francis has said when he ran Argentina’s bishops conference in the 1990s, that no such evidence existed in Church files.
The most damning accusation against Francis himself is that as the military junta took over in 1976, he withdrew his support for two slum priests whose activist colleagues in the liberation theology movement were disappearing.
The priests were then kidnapped and tortured at the Navy Mechanics School, which the junta used as a clandestine prison.
Francis said he had told the priests — Orlando Yorio and Francisco Jalics — to give up their slum work for their own safety, and they refused.
He testified as part of a human rights trial in 2010 that to save them, he persuaded another priest to fake an illness so that he could hold a private Mass for dictator Jorge Videla and personally plead for the Jesuits’ release. They were set free in October 1976, left drugged and blindfolded in a field.
Yorio, who is now dead, later accused Francis of effectively delivering them to the death squads by declining to publicly endorse their work.
But Jalics has said he and Francis have reconciled and that he considers the matter closed.
Francis’s decision to open the Church’s archives raises the question of whether he will do the same elsewhere in Latin America, where the Church was closely aligned with right-wing military dictatorships of the same period that targeted leftists in El Salvador, Chile, Nicaragua and elsewhere.