| Election Name: | 1921 Hastings by-election |
| Type: | presidential |
| Country: | United Kingdom |
| Previous Election: | Hastings (UK Parliament constituency)#Elections in the 1910s |
| Previous Year: | 1918 |
| Next Election: | Hastings (UK Parliament constituency)#Elections in the 1920s |
| Next Year: | 1922 |
| Election Date: | 4 May 1921 |
| Candidate1: | Percy |
| Party1: | Unionist Party (UK) |
| Popular Vote1: | 11,685 |
| Percentage1: | 54.7% |
| Candidate2: | Davies |
| Party2: | Labour Party (UK) |
| Popular Vote2: | 5,437 |
| Percentage2: | 25.5% |
| Candidate3: | Blackman |
| Party3: | Liberal Party (UK) |
| Popular Vote3: | 4,240 |
| Percentage3: | 19.8% |
| Map Size: | 250px |
| MP | |
| Posttitle: | Subsequent MP |
| Before Election: | Lyon |
| Before Party: | Unionist Party (UK) |
| After Election: | Percy |
| After Party: | Unionist Party (UK) |
The 1921 Hastings by-election was held on 4 May 1921. The by-election was held due to the resignation of the incumbent Coalition Unionist MP, Laurance Lyon. It was won by the Coalition Unionist candidate Eustace Percy.