| Election Name: | 1957 Auckland City mayoral by-election |
| Country: | New Zealand |
| Flag Image: | Coat of arms of Auckland.svg |
| Type: | Presidential |
| Ongoing: | no |
| Previous Election: | 1956 Auckland City mayoral election |
| Previous Year: | 1956 |
| Next Election: | 1959 Auckland City mayoral election |
| Next Year: | 1959 |
| Election Date: | 2 November 1957 |
| Turnout: | 30,944 |
| Candidate1: | Keith Buttle |
| Party1: | Citizens & Ratepayers |
| Popular Vote1: | 17,298 |
| Percentage1: | 55.90 |
| Candidate2: | John Stewart |
| Party2: | New Zealand Labour Party |
| Popular Vote2: | 7,573 |
| Percentage2: | 24.47 |
| Candidate3: | Horace Kirk |
| Party3: | Independent politician |
| Popular Vote3: | 4,906 |
| Percentage3: | 15.85 |
| Mayor | |
| Before Election: | Tom Ashby |
| After Election: | Keith Buttle |
The 1957 Auckland City mayoral by-election was held to fill the vacant position of Mayor of Auckland. The polling was conducted using the standard first-past-the-post electoral method.
The by-election was triggered by the death of sitting Mayor Tom Ashby. Five candidates put their names forward for the contest, with Deputy-Mayor Keith Buttle elected the new Mayor. Councillor Dove-Myer Robinson's United Independents (who had backed Ashby a year earlier) ticket chose to neither contest the election nor endorse a candidate.
The following table gives the election results: