From today, Mr J.Y. Pillay, chairman of the Council of Presidential Advisers (CPA), is acting president until a new president is sworn in. His role follows the completion of Dr Tony Tan Keng Yam's six-year term yesterday.
When the office of president is vacant, the first in line to exercise its powers is the CPA chairman, followed by the Speaker of Parliament.
Mr Pillay, 83, will act as president until after Polling Day on Sept 23 - or after Nomination Day on Sept 13, if a candidate is elected unopposed.
This is the first time the office has fallen vacant since the elected presidency was introduced in 1991.
The first popular election was in late August 1993, with the elected president Ong Teng Cheong taking office on Sept 1 and finishing six years later, on Aug 31. All terms since then followed this schedule.
But a move of the election to this month - to avoid a clash with National Day festivities last month - was announced this year, along with changes to the Presidential Elections Act. The move will happen only once, since the calendar stabilises again after this election.
The Government consulted the Attorney-General on the move in dates and confirmed that it "can be done under the current laws".
Mr Pillay is no stranger to exercising the powers of the president.
As CPA chairman since 2005, he has been acting president each time the president goes on an overseas trip. He acted as president in May, when Dr Tan made state visits to Europe. Mr Pillay has served more than 60 such "stints" - the longest of which was 16 days in April and May of 2007, when then President S R Nathan visited Africa.
Mr Pillay told The Straits Times that when there is an acting president, the Ministry of Foreign Affairs customarily does not organise incoming visits. But such visits have cropped up, like that of US President George W. Bush in November 2006.
Mr Pillay was a veteran civil servant, whom founding prime minister Lee Kuan Yew said was "equal to the best brains in America".
He was permanent secretary in the finance, defence and national development ministries. He was also chairman of the Singapore Exchange and DBS Bank, and managing director of GIC and the Monetary Authority of Singapore.
He, however, is best known for his role as founding chairman of Singapore Airlines (SIA). From a small fleet of just 12 aircraft when he took over in 1972, SIA grew into one of the world's top airlines by the time he stepped down in 1996.
He was modest about his achievements, noting the "simpler environment then".
He quipped: "We would do nothing and the economy would grow by 5 to 7 per cent. Now we struggle to get 2 to 3 per cent, and the electorate is much better educated."