A person who wishes to run for the office of President has to fulfil stringent qualifications set out in the Constitution, which are as follows:
He must be a citizen of Singapore.
He must not be less than 45 years of age.
His name must appear in a current register of electors.
He must be resident in Singapore at the date of his nomination for election and must have been so resident for periods amounting in the aggregate to not less than ten years prior to that date.
He must not be subject to any of the following disqualifications:
(a) being and having been found or declared to be of unsound mind;
(b) being an undischarged bankrupt;
(c) holding an office of profit;
(d) having been nominated for election to Parliament or the office of President or having acted as election agent to a person so nominated, failing to lodge any return of election expenses required by law within the time and in the manner so required;
(e) having been convicted of an offence by a court of law in Singapore or Malaysia and sentenced to imprisonment for a term of not less than one year or to a fine of not less than S$2,000 and having not received a free pardon, provided that where the conviction is by a court of law in Malaysia, the person shall not be disqualified unless the offence is also one which, had it been committed in Singapore, would have been punishable by a court of law in Singapore;
(f) having voluntarily acquired the citizenship of, or exercised rights of citizenship in, a foreign country, or having made a declaration of allegiance to a foreign country;
(g) being disqualified under any law relating to offences in connection with elections to Parliament or the office of President by reason of having been convicted of such an offence or having in proceedings relating to such an election been proved guilty of an act constituting such an offence.
He must be a person of integrity, good character and reputation.
He must not be a member of any political party on the date of his nomination for election.
He must have for a period of not less than three years held office
as Minister, Chief Justice, Speaker, Attorney-General, Chairman of the Public Service Commission, Auditor-General, Accountant-General or Permanent Secretary;
as chairman or chief executive officer (CEO) of the Central Provident Fund Board, the Housing and Development Board, the Jurong Town Corporation or the Monetary Authority of Singapore;
as chairman of the board of directors or CEO of a company incorporated or registered under the Companies Act with a paid-up capital of at least $100 million or its equivalent in foreign currency; or
in any other similar or comparable position of seniority and responsibility in any other organization or department of equivalent size or complexity in the public or private sector which has given him such experience and ability in administering and managing financial affairs as to enable him to carry out effectively the functions and duties of the office of President.
The strictness of these qualifications led to the 1999 and 2005 elections being walkovers as S.R. Nathan was the only qualified candidate on nomination day.