Smerilli, an economist, is currently the No. 2 in the Dicastery for Promoting Integral Human Development. As prefect, she replaces the retiring Canadian Cardinal Michael Czerny, who turns 80 soon.
With the appointment of Smerilli, Leo appears to be following the lead of his predecessor, Pope Francis, who made a point of promoting women to top-level management positions within the Holy See as part of his response to calls by women for greater decision-making roles in the church.
Earlier this month, Leo named a Mexican-American woman, Maria Montserrat Alvarado, to head the Vatican's communications operations.
But for more central Holy See offices like Smerilli's, Leo too is following Francis' lead by simultaneously naming Cardinal Fabio Baggio as a "pro-prefect" of the office, where he is currently undersecretary.
The dual nominations recognise that sometimes the role of a Vatican department head requires being an ordained priest and cardinal.
Baggio was also given the mandate to head up the Vatican's Borgo Laudato Si environmental educational centre, at Castel Gandolfo, near Rome.
The Catholic Church reserves the priesthood for men, and women have long complained of a second-class status despite carrying out the lion's share of the church's work running schools, hospitals and passing the faith on to younger generations.
