Below are lists of Plaid Cymru marginal seats showing which constituencies won in the latest elections can be most easily lost.
Historical
Below is the Plaid Cymru defence list consisting of Plaid Cymru held marginal seats for the 2029 general election based on the 2024 boundaries. These marginal constituencies are ordered from the most vulnerable seats to the safest.
| Rank | Constituency | Region | Majority | Swing to Defeat | |
|---|---|---|---|---|---|
| 1. | Ynys Mon | Wales | 637 | 0.98% | |
| 2. | Caerfyrddin | Wales | 4,535 | 4.97% | |
| 3. | Ceredigion Preseli | Wales | 14,789 | 15.97% | |
| 4. | Dwyfor Meirionnydd | Wales | 15,876 | 19.65% |