Roedd Sir Forgannwg yn etholaeth seneddol i Dŷ'r Cyffredin yn Senedd y Deyrnas Unedig o 1536 hyd at 1885 .
Blwyddyn
Aelod
1541
Syr George Herbert
1545
anhysbys
1547
John Thomas Bassett
1553
George Mathew
1553
Anthony Mansell
1554
Edward Mansell
1554
Syr Edward Carne
1555
anhysbys
1558
William Herbert I
1559
William Herbert I
1562/3
William Bassett
1571
William Bassett
1572
William Herbert II
1577
William Mathew
1584
Robert Sidney
1586
Thomas Carne
1588
Thomas Carne
1593
Syr Robert Sidney
1597
Syr Thomas Mansell
1601
Syr John Herbert
1604
Philip Herbert
1605
Syr Thomas Mansell
1614
Syr Thomas Mansell
1621
William Price
1624
Syr Robert Mansell
1625
Syr Robert Mansell
1626
Syr John Stradling
1628
Syr Robert Mansell
1640
Syr Edward Stradling
1640
Philip Herbert
1653
Dim cynrychiolaeth
1654
Philip Jones Edmund Thomas
1656
Philip Jones Edmund Thomas
1659
Evan Seys
1660
Syr Edward Mansel
1661
William Herbert
1670
Syr Edward Mansel
1679
Bussy Mansel
1681
Syr Edward Mansel
1689
Bussy Mansel
1699
Thomas Mansel, Barwn 1af Mansel
1712
Robert Jones
1716
Syr Charles Kemeys
1734
William Talbot
1737
Bussy Mansel
1745
Thomas Mathews
1747
Charles Edwin
1756
Thomas William Mathews
1761
Syr Edmund Thomas
1767
Richard Turbervill
1768
George Venables-Vernon
1780
Charles Edwin
1789–1814
Thomas Wyndham
1814
Benjamin Hall
1817
Syr Christopher Cole
1818
John Edwards
1820
Syr Christopher Cole
1830
Christopher Rice Mansel Talbot
Bu dim ond dri etholiad cystadleuol yn Sir Forgannwg rhwng y Ddeddf Diwygio Mawr ym 1832 a diddymu'r etholaeth ym 1885 sef etholiadau 1837, 1857 a 1874:
Wales at Westminster James, Arnold J a Thomas John E Gwasg Gomer 1981