| Election Name: | 1970 St Marylebone by-election |
| Type: | parliamentary |
| Country: | United Kingdom |
| Seats For Election: | Constituency of St Marylebone (UK Parliament constituency) |
| Ongoing: | no |
| Previous Election: | 1970 United Kingdom general election |
| Previous Year: | June 1970 |
| Election Date: | 22 October 1970 |
| Candidate1: | Kenneth Baker |
| Party1: | Conservative Party (UK) |
| Popular Vote1: | 10,684 |
| Percentage1: | 63.49% |
| Swing1: | 1.40% |
| Candidate2: | Keith Morrell |
| Party2: | Labour Party (UK) |
| Popular Vote2: | 4,542 |
| Percentage2: | 26.99% |
| Swing2: | 2.32% |
| Candidate3: | Michael Vann |
| Image3: | Lib |
| Party3: | Liberal Party (UK) |
| Popular Vote3: | 1,038 |
| Percentage3: | 6.19% |
| Swing3: | 2.41% |
| MP | |
| Posttitle: | Subsequent MP |
| Before Election: | Quintin Hogg |
| Before Party: | Conservative Party (UK) |
| After Election: | Kenneth Baker |
| After Party: | Conservative Party (UK) |
| Next Election: | February 1974 United Kingdom general election |
| Next Year: | Feb. 1974 |
The St Marylebone by-election of 22 October 1970 was held after Conservative Member of Parliament (MP) Quintin Hogg became a life peer. The seat was retained for the Conservatives by Kenneth Baker, who had lost his previous seat of Acton at the general election four months earlier; Baker would go on to represent the Mole Valley seat in Surrey and become a long-serving Cabinet minister.