The role of secretary-general of the Vatican governorate is usually held by a bishop.
Pope Francis has appointed the first-ever woman to head the governorate of the Vatican City.
Sister Raffaella Petrini will serve as secretary-general of the Governorate and become the highest-ranking woman in the world's smallest state.
The 52-year-old Italian nun will be responsible for overseeing administrative operations, including the Vatican museums, the post office, and the police.
Her new role -- similar to the deputy mayor of a city -- is traditionally held by a bishop.
Pope Francis has repeatedly said he wants women to play a bigger role in the Catholic Church to achieve greater gender equality.
He has also recently appointed women to lead areas on religious and social issues for the first time.
In August, the pope appointed another nun, Sister Alessandra Smerilli, as the interim Secretary of the Vatican's development office, which deals with justice and peace issues.
Laws were also changed in January to allow women to serve as lectors at liturgies, altar servers, and communion distributors, although Pope Francis did not say the change would open the door to women priests.