Defence Secretary Dennis Richardson has advised the PM Malcolm Turnbull of his intention to step down on May 12.
The retirement of the veteran of 48 years of public service opens up a vacancy for the high-profile position, with Associate Secretary Brendan Sargeant to serve as Acting Secretary pending the appointment of a successor.
The former Ambassador to Washington and principal advisor to PM Bob Hawke was appointed Defence Secretary in October 2012 after a two-year stint heading up the Department of Foreign Affairs and Trade from 2010-2012.
Defence Minister Senator Payne issued a statement paying tribute to Richardson's “incomparable” record of service:
“Since I have become Minister, I have never been left in any doubt about Dennis' views. His judgement, insight and unparalleled experience ensured he has been an invaluable source of counsel to me. His depth of knowledge, experience, and his plain speaking will be missed.
“Throughout his career Dennis has developed a close and respected network of friends and peers both at home and abroad. On my visits overseas as Defence Minister I have witnessed the high esteem in which he is held by officials, politicians and commentators around the world.
“I wish Dennis and his wife Betty all the best for a retirement filled with family, pets, wine and travel.”
Defence Industry Minister Christopher Pyne said he could personally attest to Richardson's “legendary frankness and fearlessness in counsel”.
“Dennis’ professionalism and integrity are the very embodiment of the spirit that has driven the Australian public service for over a century,” he said.
“His contribution to the country as Secretary of the Department of Foreign Affairs and Trade, Ambassador to the United States, the Director-General of Security and finally in his role as Secretary of the Department of Defence, will leave a lasting legacy.”