Prime Minister Malcolm Turnbull has confirmed his chief of staff Greg Moriarty has been appointed the new secretary of Defence.
The appointment, revealed by Fairfax Media this month, replaces former Defence boss Dennis Richardson and sees Mr Turnbull name his third chief of staff this year, after Drew Clarke retired in April.
Respected former diplomat Peter Woolcott will lead Mr Turnbull's office from September 4, when Mr Moriarty begins his five year term at Defence.
Mr Turnbull praised Mr Moriarty, saying he brought a considerable range and depth of experience to the role. Mr Moriarty served as the government's first counter-terrorism coordinator.
"He first worked in the Department of Defence from 1986 to 1995, primarily in the Defence Intelligence Organisation.
"He also served in the Headquarters of the United States Central Command in the Persian Gulf during operations Desert Shield and Desert Storm.
"As an officer in the Department of Foreign Affairs and Trade, Greg Moriarty served in a number of senior roles, including senior negotiator with the peace monitoring Group on Bougainville, ambassador to Iran, ambassador to Indonesia and as a deputy secretary of the department," Mr Turnbull said.
Since August 2016, Mr Moriarty was Mr Turnbull's international and national security adviser before becoming chief of staff when Mr Clarke retired.
"I thank Mr Moriarty for his outstanding work in my office in which he demonstrated his leadership and strategic understanding as he has done throughout his career," Mr Turnbull said.
"I also thank Brendan Sargeant for his dedicated service while acting in the role of secretary of the Department of Defence."
Shadow defence spokesman Richard Marles said Labor welcomed Mr Moriarty's appointment.
"This is a role with tremendous responsibility, and Labor looks forward to working with Mr Moriarty in our traditional spirit of bipartisanship to advance Australia's national security," he said.
Mr Turnbull said Mr Woolcott's extensive experience made him highly qualified to lead the Prime Minister's office.
Chief of staff to former foreign minister Alexander Downer, Mr Woolcott has serve since February 2016 as Australia's High Commissioner to New Zealand.
From 2014 to 2016 he was special ambassador for the environment , and is a former permanent representative to the United Nations in Geneva and ambassador for nuclear disarmament, ambassador for people smuggling issues and ambassador to Italy.
His departure from New Zealand could open the way for Attorney-General George Brandis, who is reportedly being considered for the role.
Immigration and Border Protection chief Mike Pezzullo, Australian Strategic Policy Institute boss Peter Jennings, Health Department head Martin Bowles and Department of Human Services secretary Kathryn Campbell were all reportedly considered for Defence's top job.
The role of Defence secretary is equal in rank to the Chief of the Defence Force – currently Air Chief Marshal Mark Binskin – under an arrangement known as the diarchy.