Pope Francis has for the first time appointed a woman to a high office in the state administration of Vatican City.
As the head of the governorate of the Vatican, Franciscan Sister Raffaella will oversee administrative operations such as the Vatican museums, post office and police.
The role makes the 52-year-old nun the highest-ranking woman in the city-state.
Petrini is a Rome native and has served on the Congregation for the Evangelization of Peoples since 2005. She received a political science degree from the Libera Università Internazionale degli Studi Social Guido Carli and a PhD from the Pontifical University of St. Thomas Aquinas, where she teaches.
According to an online newspaper, The National Catholic Reporter, the position of Head of governorate of the Vatican is traditionally held by a bishop.
Francis, 84, has repeatedly said he wants women to play a greater role in the Roman Catholic Church.
In January he changed the law to allow them to serve as readers at liturgies, altar servers and distributors of communion — but stopped short of saying the change could one day open the door to female priests.
In February he broke with Catholic tradition to appoint a woman as an undersecretary of the synod of bishops, the first to hold the post with voting rights in a body that studies major questions of doctrine.
The pope created a commission in 2016 into the history of female deacons in the early year of the Catholic Church, in a move reformers hope could open the door to women taking up the role today.
The pope said women have made a "precious contribution" to the church, but the new law merely formalizes roles that women have already been taking in numerous countries, including the United States.
In addition to elevating Petrini, the pope appointed lawyer Giuseppe Puglisi-Alibrandi as deputy secretary-general of the governorate.