The 1972 Merthyr Tydfil by-election of 13 April 1972 was held after the death of S. O. Davies on 25 February the same year. The Labour Party won the by-election in what had traditionally been a safe seat, although Davies had been elected in the 1970 general election as an Independent after he had been deselected due to his age.
| Party | Candidate | Votes | % | ±% | |
|---|---|---|---|---|---|
| Labour | Edward Rowlands | 15,562 | 48.5 | +19.8 | |
| Plaid Cymru | Emrys Roberts | 11,852 | 37.0 | +27.4 | |
| Conservative | Christopher Barr | 2,336 | 7.4 | −2.4 | |
| Communist | Arthur Lewis Jones | 1,519 | 4.7 | N/A | |
| Liberal | Angus Donaldson | 765 | 2.4 | N/A | |
| Majority | 3,710 | 11.5 | N/A | ||
| Turnout | 32,034 | 79.5 | +1.6 | ||
| Registered electors | 30,202 | ||||
| Labour gain from Independent | Swing | ||||