He named Cardinal Peter Kodwo Appiah Turkson, of Cape Coast, Ghana, to head the justice and peace commission, a position roughly equivalent to justice minister.
Turkson, 61, Ghana's first cardinal, becomes only the second African to head the body, which advises the Pope and the Vatican on justice issues and prepares documents on topics such as human rights, immigration and law.
He has just completed a high-profile stint as the relator, or secretary-general, of the three-week synod on Africa that ends on Sunday, and has been tipped in Church circles to be a strong candidate for the papacy after the death of Benedict.
Turkson's new appointment will give him increased visibility in the Roman Catholic Church and around the world.
The Catholic Church is growing faster in Africa than on any other continent and Turkson has years of experience in relations with Islam, an attribute that should stand him in good stead for a shot at the papacy.
He was born in Ghana and educated there as well as in the United States. At the start of the synod three weeks ago, Turkson was asked if, after Barack Obama became the first black US president, the next pope could be an African. He answered: "Why not?"
There have been only two African popes in the history of the Church, the last in the fifth century.