All of the vacancies were related to Barisan Sosialis resignations, which continued into the following year, with the sole exception being Joo Chiat's MP Fong Kim Heng.

On 8 December 1965, about four months into independence, the Barisan Sosialis began to boycott Parliament in response to the current legislature and its democracy as "phony".

The first MP to resign was Lim Huan Boon on 31 December 1965, after which by-election nominations were called for Bukit Merah on 8 January.

A further two seats became vacant nine months later on 7 October, with the resignations of Chia Thye Poh and Lee Tee Tong.

Chua Chu Kang, Crawford and Paya Lebar constituencies were at stake in the second by-election, with nominations occurring on 1 March.