The 1936 Llanelli by-election was held on 26 March 1936. The by-election was held due to the death of the incumbent Labour MP, John Henry Williams. It was won by the Labour candidate Jim Griffiths.[1]
| Party | Candidate | Votes | % | ±% | |
|---|---|---|---|---|---|
| Labour | Jim Griffiths | 32,188 | 66.8 | N/A | |
| National Liberal | William Albert Jenkins | 15,967 | 33.3 | N/A | |
| Majority | 16,221 | 33.5 | N/A | ||
| Turnout | 48,155 | 68.4 | N/A | ||
| Registered electors | 70,380 | ||||
| Labour hold | Swing | ||||