Australia's most senior Catholic cleric will turn 75 and according to Vatican protocols, introduced by the Pope in 2014, is obliged to tender his resignation  .

But this does not mean the controversial churchman, who has given evidence three times at the child abuse royal commission about sexual abuse by clergy, will leave his job as the Vatican's Prefect of the Secretariat for the Economy - Vatican treasurer - any time soon.

The Pope does not have to accept Dr Pell's resignation and last month Pope Francis confirmed he would stay on as the Vatican’s top financial official until at least 2019.

Cardinal Pell faced intense scrutiny across the world for both his role in the Vatican’s financial reform and his response to allegations of child sexual abuse cases as a priest and bishop in Ballarat and Melbourne. 

The Pope has already backed him twice when his reform methods drew complaints from some powerful figures in Rome.

The resignation of a cardinal can be a drawn-out process. While the Pope can accept or reject it immediately, an immediate announcement one way or the other is unlikely.

Observers say it is a high probability the Australian cardinal will stay on for another few years, given his crucial role in reforming the Vatican's medieval financial structure.

Dr Pell met with Pope Francis after this first day of evidence from Rome in March and said then he had the pontiff's full confidence.

In early March, Cardinal Pell testified before the Royal Commission into Institutional Responses to Child Sexual Abuse from Rome. The inquiry examined complaints that Cardinal Pell had failed to act on situations of abuse when he was a priest in the Ballarat diocese and later in his role as the Archbishop of Melbourne. Pell vigorously denied the charges. 

Earlier this year, Cardinal Pell made an impassioned public pledge to help those in Ballarat "wounded by the scourge of sexual abuse", in the final act of his appearance at the child sex abuse Royal Commission.

"One suicide is too many, and there have been many such tragic suicides," the cardinal said on the doorstep of the Rome hotel where over four nights he was grilled about what he knew of paedophile priests in Melbourne and Ballarat in the 1970s and 1980s.