Cardinal George Pell, financial adviser to the Vatican, is testifying in Rome, answering questions via video link from Australia's Royal Commission.
The arrangements were made after the 74-year-old Pell asked to be excused from traveling home to Australia to testify because of a heart condition that made flying complicated.
His testimony will begin just hours before 'Spotlight,' a film about the newspaper, the Boston Globe's investigation into the churches role in moving along paedophile priests, waits to hear if it has won the Oscar for best picture.
Spotlight premiere in London
Cardinal Pell has appeared before the Royal Commission into Institutional Responses to Child Sexual Abuse twice before.
It is the highest form of investigation in Australia, and will be examining if and how the Catholic Church, as well as other bodies, dealt with decades of alleged abuse across Australia.
The body cannot bring criminal charges, but it has the power to recommend referring individual cases to police and prosecutors.
Cardinal Pell faces allegations that he mishandled cases of abusive clergy when he was archbishop of Melbourne and then later Sydney, where he led the Australian church until Pope Francis named him the Vatican's finance manager in 2014.
Pell denies the accusations and has said sorry to victims for what he calls the "profoundly evil" actions of some priests.
Those that stand behind Pell say he has been made a scapegoat for a problem that began long before him, however alleged victims claim he had the power to stop wrongdoing.
In 2015 seven Australian archbishops released a statement: "He is a man of integrity who is committed to the truth and to helping others, particularly those who have been hurt or who are struggling."
The Washington Post has reported that previous Australian inquiries concluded that Cardinal Pell created a victims' compensation scheme with the intention of limiting the church's liability.
Alleged abuse survivors in Australia have been angered by Pell's request to answer questions from Rome and more than a dozen survivors are traveling to Rome to be on hand for the testimony.
Their trip is the result of crowdfunding initiative that raised more than $200,000 Australian, around £103,000.
Speaking to The Washington Post Dr Cathy Kezelman, president of Adults Surviving Child Abuse, a support group in Australia, said lots of anger is directed at Pell from alleged victims who see him as representing the things that were, and are, wrong with the Australian church.
She said: "He is in a position of great power and a symbol of a hierarchy and a system of power which to many repeatedly failed them and continues to do so with perceived hollow apologies, lack of contrition but more so, no real accountability."
