| Election Name: | 1921 Westminster St George's |
| Type: | presidential |
| Country: | United Kingdom |
| Previous Election: | Westminster St George's (UK Parliament constituency)#Elections in the 1910s |
| Previous Year: | 1918 |
| Next Election: | Westminster St George's (UK Parliament constituency)#Elections in the 1920s |
| Next Year: | 1922 |
| Election Date: | 7 June 1921 |
| Candidate1: | Erskine |
| Image1: | James Erskine crop.jpg |
| Image1 Size: | 85px |
| Party1: | Anti-Waste League |
| Popular Vote1: | 7,244 |
| Percentage1: | 57.5 |
| Candidate2: | Jessel |
| Image2 Size: | 85px |
| Party2: | Unionist Party (UK) |
| Popular Vote2: | 5,356 |
| Percentage2: | 42.5 |
| Map Size: | 250px |
| MP | |
| Posttitle: | Subsequent MP |
| Before Election: | Long |
| Before Party: | Unionist Party (UK) |
| After Election: | Erskine |
| After Party: | Anti-Waste League |
The Westminster St George's by-election of 1921 was held on 7 June 1921.[1] The by-election was held due to the elevation to the peerage of the incumbent Coalition Conservative MP, Walter Long. It was won by the Anti-Waste League candidate James Malcolm Monteith Erskine.