Pope Francis has chosen a bishop who is a trusted theological adviser from his Argentine homeland for one of the Vatican’s most powerful positions – head of the watchdog office that ensures doctrinal orthodoxy.

Monsignor Victor Manuel Fernandez, now serving as archbishop of La Plata, Argentina, is tapped to head the Dicastery, or department, for the Doctrine of the Faith.

The new doctrinal prefect, or chief, has been nicknamed the “pope’s theologian” since he is widely believed to have helped author some of Francis’ most important documents.

The office enforces orthodoxy of church teaching and disciplines theologians deemed to have strayed from Catholic doctrine in their lectures or publications.

But the office has taken on considerably more importance in recent decades to rank-and-file faithful as the stain of paedophile priests spread across the globe.

Pope Francis
Pope Francis has appointed a fellow Argentine to the role (AP)

Among the department’s duties are evaluating and processing sex abuse allegations against clergy.

Msgr Fernandez is widely believed to have been a key author behind some of Francis’ most consequential documents, notably “God is Love”, a 2016 exhortation that opened the door to letting divorced Catholics who remarry in civil ceremonies to receive Communion.

Catholic teaching holds that marriage is a sacrament, and that remarried Catholics must live together as brother and sister and abstain from sex as a condition for receiving Communion.

That prospect – long sought by divorced and remarried Catholics who lament being cut off from the Eucharist – would anger conservative hierarchy and rank-and-file faithful if it were to be codified in teaching some day.

The new chief replaces retiring Cardinal Luis Ladaria, a Jesuit like Francis who took over in 2017, after the pontiff abruptly removed conservative German Cardinal Gerhard Mueller after a single term as the doctrinal watchdog.

Cardinal Mueller had been appointed to that post by Pope Benedict XVI, a darling of church conservatives.

Msgr Fernandez, 60, will take up his post in mid-September, the Vatican said.

The Pope celebrates Mass
Pope Francis presides over a mass on St Peter and St Paul’s Day last week (AP)

He is a prolific author and biblical expert who has long had support of Francis, who before becoming pontiff in 2013, was Cardinal Jorge Mario Bergoglio, archbishop of Buenos Aires.

Msgr Fernandez has made clear that while archbishop of Buenos Aires, Cardinal Bergoglio supported his nomination as rector of the Catholic University of Argentina after critics raised concerns about some of his doctrinal positions.

The doctrinal watchdog office has 16th-century roots in a commission established to deal with heresy and schism.

Known originally as the Sacred Roman and Universal Inquisition, the body also scrutinised matters of faith and morals.

In a letter to his new appointee that was made public by the Vatican on Saturday, Francis wrote that the office in its current version has as its “central purpose” safeguarding church teaching that springs from faith in order to “give reason for our hope, but not as enemies who point out and condemn”.