The head of the federal Finance Department has shocked staff, telling them he will step down within a month.
David Tune emailed his employees at lunch-time on Friday, saying he will retire on June 27.
The career public servant has led the central department, which helps to control government spending, for almost five years.
Finance was his first posting as a departmental secretary, but it is understood he told his minister, Mathias Cormann, months ago that he wanted to finished his career this year.
"Having been a public servant for over 38 years and having just turned 60, I have been thinking for a while that now is the right time, following another budget, to 'hang up the boots' and do something different with my life," Mr Tune told staff on Friday.
"Some of you will have heard me say on occasions that I am very proud to have been a public servant. What we do in the [Australian Public Service] really matters to the lives of the Australian people. The opportunities I have had to contribute to that over the years are ones that I will always cherish."
He said he and his wife had planned a long trip overseas, and he looked forward to being an "armchair observer over the coming years".
Prime Minister Tony Abbott is expected to announce Mr Tune's successor shortly.
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Mr Tune drew widespread attention on Thursday when he told a Senate estimates hearing the previous Rudd government had forced him to approve its controversial advertising campaign about asylum seekers during the election campaign, despite concerns about whether it breached the caretaker conventions.
"I had to obey, as a public servant, a legal direction and I did so," he told the committee.
Mr Tune will be the fourth department head to leave the Abbott government, which sacked three secretaries shortly after it won office: Agriculture chief Andrew Metcalfe, Resources' Blair Comley and Industry's Don Russell.
The government also initially told Treasury secretary Martin Parkinson to leave mid-way through this year, though he has since been asked to stay until the G20 meeting in November has finished.
Senator Cormann praised his outgoing secretary, noting the "great support and wise counsel" he provided ministers during the preparation of the budget.
"David Tune is an outstanding public servant who has served governments of both political persuasions with great distinction," the minister said.
"He has made an enormous contribution to public policy and government administration for Australia across a wide range of areas over the last 38 years."
Mr Tune's former minister, Labor senator Penny Wong, also thanked for secretary for bringing his "commitment, professionalism and humanity to his work".
"His sustained contribution to public policymaking has been profound. The Australian Public Service is poorer for his leaving."