The top civil servant at the Ministry of Defence, Mr Chiang Chie Foo, will step down on Sept 1.
The 56-year-old will retire from the Administrative Service after 32 years of service in the public sector, a statement from the Prime Minister's Office on Monday said. He has held the post since 2004.
Mr Chan Yeng Kit, 48, who became Permanent Secretary (Defence Development) last year, will be re-designated Permanent Secretary (Defence) on the same date.
After his retirement, Mr Chiang will continue to contribute to the public sector as chairman of the Central Provident Fund Board.
Mr Chan, who joined the Administrative Service in 1989, has served in various capacities in the ministries of trade and industry, defence and education.
He was appointed chief executive officer of InfoComm Development Authority of Singapore in 2005 and Permanent Secretary (Information, Communications and the Arts) in 2008.