Held as Singapore's merger with Malaysia was impending, this GE is remembered as PAP's most hard-fought election ever in history. With 39 seats after two by-election defeats and two defections to UPP, PAP expelled 13 of its own Assembly Members a week after they mutinied in a no-confidence motion on 20 July 1961. This left it hanging onto a slim one-seat majority of 26 to the opposition's 25. The dissidents formed a new party, BS, which PAP alleged was a communist front. On 3 July 1962, while the National Referendum debate was ongoing, another PAP AM Hoe Puay Choo resigned, leaving it one seat short against opposition. She joined BS on 11 August 1962. Five days later, UPP's S. V. Lingam returned to PAP's fold and it regained its one-seat advantage. Another five days later, PAP Minister Ahmad Ibrahim passed away from liver cancer, leaving a 25 to 25 stand-off in the legislature. BS planned to field its iconic leader, Lim Chin Siong, in the vacated seat but Prime Minister Lee Kuan Yew decided against a by-election, choosing instead to call a GE to court a fresh mandate. PM Lee surmised that if PAP did not win, the Malaysia Federal authorities could deal with a pro-communist ruling party in Singapore. Before the GE, the PAP government launched Operation Coldstore on 2 February 1963 and detained several BS leaders, including Lim. Sole WP AM David Marshall resigned from the party he founded and became independent. Once again, PAP fielded a full slate and was challenged by three camps with enough candidates to also run for power. BS and its partner PR covered all except two seats. UPP surprised many with a large slate. SA, a formalised umbrella of SPA, UMNO, MCA and MIC, was endorsed by Malaysia's ruling Alliance Party coalition. SPA provided two-thirds of SA's candidates but several leaders including former Chief Minister Lim Yew Hock sat out. In the end, PAP managed to eke out an election victory with a two-thirds majority and captured all wards previously won by SA in 1959. All except in three constituencies saw a record of 92 candidates forfeit their deposits. Also, the presence of independent legislators came to an end. To discourage rampant defections in future, the PAP government passed a law stipulating that legislators will lose their seats if they resign or are expelled from the political parties that they were elected under. The following year in 1964, PAP officially registered itself in Malaysia and contested the general election in the Federation, escalating its differences with the Alliance Party. In that same year, former AM and defeated SA candidate, A. P. Rajah, was brought back into the legislature as Speaker and served for two years until 1966.

Old Assembly dissolution: 3 September 1963 [Tue]
Nomination day: 12 September 1963 [Thu]
Polling day: 21 September 1963 [Sat]
New Assembly convention: 22 October 1963 [Tue]

Electorate: 617,650
Voter turnout: 587,433 (95.1%)

Election deposit: $500

Aljunied Geylang Serai Moulmein Southern Islands
Anson Geylang West Mountbatten Stamford
Bras Basah Havelock Nee Soon Tampines
Bukit Merah Hong Lim Pasir Panjang Tanglin
Bukit Panjang Jalan Besar Paya Lebar Tanjong Pagar
Bukit Timah Jalan Kayu Punggol Telok Ayer
Cairnhill Joo Chiat Queenstown Telok Blangah
Changi Jurong River Valley Thomson
Chua Chu Kang Kallang Rochore Tiong Bahru
Crawford Kampong Glam Sembawang Toa Payoh
Delta Kampong Kapor Sepoy Lines Ulu Pandan
Farrer Park Kampong Kembangan Serangoon Gardens Upper Serangoon
Geylang East Kreta Ayer Siglap
Total seats = 51