 Singapore immediately sought international recognition of its sovereignty . The new state joined the United Nations on 21 September 1965 , becoming the 117th member ; and joined the Commonwealth in October that year . Foreign minister Sinnathamby Rajaratnam headed a new foreign service that helped assert Singapore 's independence and establishing diplomatic relations with other countries . On 22 December 1965 , the Constitution Amendment Act was passed under which the Head of State became the President and the State of Singapore became the Republic of Singapore . Singapore later co @-@ founded the Association of Southeast Asian Nations ( ASEAN ) on 8 August 1967 and was admitted into the Non @-@ Aligned Movement in 1970 . 
