Singapore, officially the State of Singapore, was one of the 14 states of Malaysia from 16 September 1963 to 9 August 1965. At the time of merger, Singapore was a British colony (having achieved self-governance in 1959) and had previously been part of the Straits Settlements until 1946. As part of Malaysia, Singapore was the smallest state with a land area of but had the largest population of 1.82 million.

Malaysia was formed on 16 September 1963 through the merger of the Federation of Malaya with the former British colonies of North Borneo (Sabah), Sarawak and Singapore. The merger was supported by the British, Malayan and Singaporean leaders as a measure to counter communist influence in Southeast Asia. Through the 1962 integration referendum and the Malaysia Agreement, Singapore was given higher autonomy in education and labour, with the Federal Government in Kuala Lumpur overseeing defence and external affairs. Singapore was allocated only 15 seats in the Dewan Rakyat, and a reciprocal arrangement prevented citizens on either side from voting or contesting in the other's elections. These constitutional rules ensured the island's autonomy while limiting the influence of Singapore's Chinese-majority population on national politics.

However, political, racial and economic conflicts soon emerged between the governments of Singapore and Malaysia, led by the People's Action Party (PAP) and the Alliance Party respectively. Despite the agreement, both sides contested in each other's arenas: the Singapore branch of the Alliance in 1963, and the PAP in 1964. Furthermore, communal tensions between the Malay and Chinese populations in Singapore led to race riots later that year. The PAP's criticisms of the Federal Government's tax proposals in 1964 and the delay in Sabah development loans led to threats from then Finance Minister for Malaysia Tan Siew Sin to raise Singapore's revenue contribution from 40 to 60 per cent. Despite negotiations at constitutional rearrangements, Malaysian prime minister Tunku Abdul Rahman opted to resolve the disagreements by separating Singapore from the Federation, a decision supported by Singapore's finance minister Goh Keng Swee and a few PAP leaders. The Separation Agreement was signed on 7 August 1965, and Singapore became a sovereign state on 9 August.

Following separation, Malaysia supported Singapore's entry into the United Nations and the British Commonwealth. Both nations continued to share a national carrier, Malaysian Airways – renamed Malaysia–Singapore Airlines in 1966 – until the airline's split in 1971. The Singapore dollar and the Malaysian ringgit, along with the Brunei dollar, were also interchangeable with each other under the Currency Interchangeability Agreement until Malaysia withdrew in 1973. The historical narrative, particularly in Singapore due to limited public information, taught that the country had been abruptly expelled from Malaysia. This perception was shaped by a lack of detail regarding the separation talks and the sudden announcement of independence. The public release of the Albatross file in December 2025, containing Goh's records of the negotiations, provides a fuller account.

History

Post-war British Singapore

Singapore returned to British rule following the end of World War II in 1945, during which it was occupied by the Japanese. In September that year, Singapore became the headquarters of the British Military Administration under Lord Louis Mountbatten. While the British had decided to form the Malayan Union comprising both the federated and unfederated Malay states as well as the former Straits Settlements of Penang and Malacca in 1946, no clear administrative arrangements were made for Singapore. Despite objections from colonial officials and businessmen who warned that separating Singapore would damage Malaya economically, the Colonial Office argued that any future union should be voluntary rather than imposed on communities with divergent interests. The inclusion of Singapore in the Malayan Union was opposed by Malay nationalists, who viewed Singapore's Chinese-majority population as a "threat" to the political and social position of the Malays in Malaya.

The British began planning to consolidate their colonies into a larger federation anchored on Malaya, a strategy known as the "Grand Design", which Selkirk, the High Commissioner of the United Kingdom to Singapore, described as the "ultimate aim of British policy in Southeast Asia". The plan sought to maintain British influence during decolonisation while countering communist threats in the region. As Singapore gained self-governance, many local leaders viewed merger with Malaya as the city-state's only viable future, with independence disregarded as an unrealistic option. Despite overtures by Singapore's chief ministers David Marshall and Lim Yew Hock towards Malayan leader Tunku Abdul Rahman, Tunku was not keen in bringing Singapore into the Malayan Union.

The People's Action Party (PAP), led by Lee Kuan Yew, formed Singapore's fully-elected government after their victory in the 1959 Singaporean general election. The PAP and Lee continued to press for merger, which Singaporean historians cited by Tan Tai Yong attribute in part to the party's political difficulties. Lee believed that curbing the PAP's militant left-wing faction would help secure the Tunku's support for merger, yet without merger he lacked the means to defeat the faction. To reassure the Tunku and address Malay concerns in Malaya over Singapore's Chinese-majority population, the PAP established a Malay Affairs Bureau headed by Othman Wok and an Internal Security Council to oversee internal security in self-governing Singapore. In addition, to encourage a "pan-Malayan outlook" in Singapore and to show acceptance of the Malays' special status, Singapore adopted Malay as its national language, a Malay-language national anthem and appointed Yusof Ishak, an ethnic Malay, as Singapore's head of state.

Merger negotiations

In May 1961, the Tunku announced the idea of a larger union, which would also include the Borneo Territories of Sabah, Sarawak and Brunei. According to Selkirk, Lee had been advocating a merger through a broader political association that included Borneo. Lee had also circulated his paper on the British "Grand Design", warning the British and Malayan authorities that abandoning merger could allow power in Singapore to fall to a group aligned with communist China, thereby threatening British interests and security in Southeast Asia. Historians Tan Tai Yong and Mohammad Noordin Sopiee believed that the challenges to Lee's leadership, particularly PAP's losses in the 1961 by-elections, compelled the Tunku to reevaluate his opposition to Singapore's inclusion in the Federation, as he acknowledged that an independent Singapore under communist control would pose problems for Malaya. Incorporating Singapore into Malaya would allow the Tunku to directly address the communist threat in Singapore as an internal security issue.

Following a meeting between Lee and Tunku in August 1961, both agreed that Singapore would retain local autonomy on education and labour, with Malaya responsible for security, defence and external affairs. In response to the announcement, David Marshall of the Workers Party called for the Legislative Assembly to convene immediately to debate the merger, while the Barisan Sosialis (BS) condemned Lee's actions as "most irresponsible", accusing him of attempting to "cut a deal" over Singapore's constitutional future with Malaysia. The BS also called for "complete merger" or a confederal relationship that would allow Singapore to retain control over internal security. However, Lee regarded the BS's demands as attempts to "prevent [the PAP] from settling fair terms and conditions for merger". From 13 September to 9 October, Lee delivered a series of radio talks aimed at persuading the electorate of the proposed merger arrangements. On 21 September, finance minister Goh Keng Swee announced that a referendum would be held on merger with Malaya. Goh also warned that "complete merger" would strip half of Singapore's electorate of their political rights, as they would not qualify for Malaysian citizenship.

On 16 October, the Tunku compared his envisioned relationship between Malaysia and Singapore as similar to that between the United Kingdom and Northern Ireland, with local autonomy in all areas except security, defence and external affairs. A draft of the White Paper on merger was completed on 26 October, with the merger date set for June 1963. Although the White Paper provided for a common nationality for Singapore and Malayan citizens, Singapore's residents would hold a differentiated form of citizenship after the merger. This arrangement was intended to restrict voting in their respective territories. However, the BS and other opposition groups derided the proposal as a one-sided arrangement against Singaporeans' interests, warning that Singapore citizens would be relegated to "second-class" status within Malaysia. They further argued that, while the Borneo territories were granted both federal citizenship and autonomy in certain areas, the PAP had traded away Singapore's rights for what they described as "illusory autonomy" in labour and education.

Lee argued in an aide-memoire to the Tunku that Singapore should be offered the same terms as the Borneo Territories and proposed renaming "Singapore Citizen (National of the new Federation)" to "Citizen of the new Federation (Singapore)", which Lee believed would secure "a major psychological victory" among the Singaporean Chinese. Although the change was largely nominal and voting rights remained restricted, the Malayan delegation in London accepted it, granting Singapore citizens all other federal rights in Malaysia. On 14 August 1962, Lee announced that all Singaporean citizens would automatically become Malaysian citizens, rather than sharing a common nationality, and set the merger referendum for 1 September. An overwhelming majority voted for Option A, which granted Singapore the highest level of autonomy with special status as outlined in the White Paper.

Ahead of the Brunei revolt, Lim Chin Siong of BS met with its leader A. M. Azahari, and the party expressed support for the uprising. The PAP regarded these actions as a Communist-backed threat to Singapore. Using this pretext, Lee, with Malayan and British authorities, launched Operation Coldstore on 2 February 1963, detaining 113 left-wing leaders and crippling the Barisan and Communist networks. The crackdown cleared the way for further merger negotiations, though Lee, Goh, and their team still faced tough discussions with Malayan officials over the financial terms of the merger and the common market. A final agreement was reached in July 1963 following a series of meetings in London mediated by Duncan Sandys, the Secretary for Common Relations. On 16 September 1963, Singapore joined Malaya, along with Sabah and Sarawak, to form Malaysia.

Singapore in Malaysia

Shortly after merger, Singapore held its general elections on 21 September, which were also contested by the Singapore Alliance, the local counterpart of the ruling Alliance Party in Malaya. Although the Tunku and Lee had a gentlemen's agreement not to interfere in each other's politics, the Malaysian leaders, including the Tunku, had come to Singapore to campaign for the Singapore Alliance. Nevertheless, the Singapore Alliance failed to win any seats in the 1963 elections, much to the Tunku's shock. Australian and British officials regarded the PAP's victory as a public endorsement of merger and Lee's socio-economic policies.