Y gwahaniaeth rhwng diwygiadau o "Sir Forgannwg (etholaeth seneddol)"

|-
| 1837
|style="background-color: {{Conservative Party (UK)/meta/color}}" |
| [[Edwin Wyndham-Quin]]
| [[Y Blaid Geidwadol (DU|Ceidwadol)]]
| <!-- party -->
|-
| 1851
|style="background-color: {{Conservative Party (UK)/meta/color}}" |
| [[George Tyler]]
| [[Y Blaid Geidwadol (DU|Ceidwadol)]]
| <!-- party -->
|-
| 1857
|style="background-color: {{Liberal Party (UK)/meta/color}}" |
| [[Henry Hussey Vivian]]
| [[Y Blaid Ryddfrydol (DU)|Rhyddfrydol]]
| <!-- party -->
|-
| [[1885]]
Defnyddiwr anhysbys