| Election Name: | 1957 Singaporean by-elections |
| Country: | Singapore |
| Flag Year: | 1957 |
| Flag Image: | Flag of Singapore (1952–1959).svg |
| Type: | legislative |
| Vote Type: | popular |
| Election Date: | 29 June 1957 |
| Previous Election: | 1952 Seletar by-election |
| Previous Year: | 1952 |
| Next Election: | 1961 Singaporean by-elections |
| Next Year: | 1961 |
| Seats For Election: | 2 seats to the Legislative Assembly of Singapore |
| Registered: | 29,563 |
| Turnout: | 12,874 (43.55%) 11.16% |
| Leader1: | Lee Kuan Yew |
| Party1: | People's Action Party |
| Seats1: | 1 |
| Popular Vote1: | 4,707 |
| Percentage1: | 36.99% |
| Swing1: | 4.18% |
| Leader2: | Tan Chye Cheng |
| Party2: | Liberal Socialist Party (Singapore) |
| Seats2: | 1 |
| Seat Change2: | 1 |
| Popular Vote2: | 3,657 |
| Percentage2: | 28.74% |
| Swing2: | 7.52% |
| Leader3: | Lim Yew Hock |
| Party3: | Labour Front |
| Seats3: | 0 |
| Seat Change3: | 1 |
| Popular Vote3: | 1,118 |
| Percentage3: | 8.79% |
| Swing3: | 13.78% |
| Image4 Size: | 150x150px |
| Party4: | Malay Union |
| Seats4: | 0 |
| Popular Vote4: | 983 |
| Percentage4: | 7.73% |
| Swing4: | 7.73% |
| Assemblymen | |
| Posttitle: | Elected Assemblymen |
A by-election was held on 29 June 1957, with nomination day occurring on 18 May 1957 in both the constituencies of Cairnhill and Tanjong Pagar. Ultimately, Labour Front lost the Cairnhill seat to the new Liberal Socialist Party candidate Soh Ghee Soon, while Tanjong Pagar incumbent Lee Kuan Yew retained his seat.
The by-election had a voter turnout of merely 43.55%, the lowest of any elections during the period between 1948 and 1959. With the introduction of compulsory voting in 1959, the turnout of 43.55% remains the lowest for any elections in Singapore's history.
When talks with the British authorities for self-governance fell, Chief Minister David Marshall resigned his Cairnhill seat and his Labour Front party membership on 7 June 1956; LF representative Keng Bang Ee was fielded as a candidate.
The seat of Tanjong Pagar was vacated when Lee Kuan Yew resigned his seat when Marshall publicly challenged Lee in a by-election, in which Lee accepted. Marshall withdrew his bid prior to nominations citing pressured by speculations of a street protest; Chong Wei Ling became the candidate in Marshall's place.
Ahead of the election, the Singapore Malay Union (SMU) was expelled by its alliance partners consisted of UMNO and MCA. Tengku Muda, a candidate for Cairnhill, was considered by the elections department of Singapore to view him as another independent candidate.