The 1909 South Armagh by-election was held on 5 November 1909. The by-election was held due to the death of the incumbent Irish Parliamentary MP, William McKillop. It was won by the Irish Parliamentary candidate Charles O'Neill.[1]
| Party | Candidate | Votes | % | ±% | |
|---|---|---|---|---|---|
| Irish Nationalist | Charles O'Neill | 3,160 | 66.00 | N/A | |
| Irish Unionist | Richard Best | 1,628 | 34.00 | New | |
| Majority | 1,532 | 32.00 | N/A | ||
| Turnout | 4,788 | 68.17 | N/A | ||
| Irish Nationalist hold | Swing | N/A | |||