The Pope accepted Milone's request, the Vatican announced June 20, after Milone personally presented it to the Pope a day earlier.
"While wishing Milone the best in his future endeavours, the Holy See wishes to inform (everyone) that the process of naming a new director of the auditor-general's office will be underway as soon as possible," the Vatican's written statement said.
Pope Francis named Milone to fill the new position of auditor general in June 2015, more than a year after establishing special structures to oversee the Vatican's finances – the Council for the Economy and the Secretariat for the Economy.
The auditor general has the power to audit the books of any Vatican office and reports directly to the Pope. The auditing office currently has 12 people on staff.
Milone, 68, an Italian accountant and expert in corporate risk management, was born in Holland and educated in London. He was chairman and managing partner of Milone Associates and had worked for Falck Renewables, Wind Telecom and Fiat. Until 2007, he was chairman of Deloitte Italy and served three years as a member of the audit committee of the United Nations' World Food Program.
An independent auditor was a key part of the "separation of powers" necessary for reforming the Vatican's economic activity, Cardinal George Pell, prefect of the Secretariat for the Economy, wrote in 2015.
"These reforms are designed to make all Vatican financial agencies boringly successful, so that they do not merit much press attention," the cardinal wrote.
No reason was given for Milone's request to step down.
In an interview in March with the Italian daily, Corriere della Sera, Milone said the previous 18 months had been very busy because he had to learn the way things had worked and then oversee 120 offices and foundations that make up the Roman Curia or are associated with the Holy See.
The office had just been completing preliminary studies of all the major assets, finances and economic data of 2015 and 2016. "The next step is auditing the balance sheet up to Dec. 31, 2017, so as to be able to get ready for auditing the whole budget ending Dec. 31, 2018," he said.
He felt their efforts had paid off by bringing in "a new model of managing the budget and introducing the best international standards," adding that the real work in reform was, "first of all, cultural."
When asked if he had met with any resistance, he said, "more than real or actual resistance, often it was about being unaware" of more modern, integrated and transparent accounting standards. They did a lot of training to help people "overcome foreseeable difficulties," he said.
He said he never regretted accepting the job, which had been offered to him by an international headhunting agency, he said. "On the contrary, I will go all the way with great enthusiasm."
He said, "I am very motivated by the privilege of being at the service of the Pope ... and to be able to do my small part of a decisive reform for the Vatican ... A reform whose full extent has perhaps still not been well understood."
Back in September 2015, an employee of the auditor general's office notified Vatican police that Milone's computer had been tampered with, the investigation into that tampering led to the second VatiLeaks investigation and trial, according to Vatican Radio.
That trial found Msgr. Lucio Vallejo Balda, secretary of the Prefecture for the Economic Affairs of the Holy See, and Francesca Chaouqui, a member of the former Pontifical Commission for Reference on the Economic-Administrative Structure of the Holy See, guilty of having roles in the leaking of confidential documents about Vatican finances and acquitted an associate and two journalists.