Southern Monmouthshire was a parliamentary constituency in Monmouthshire, Wales. It returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom.

The constituency was created by the Redistribution of Seats Act 1885 for the 1885 general election, which divided into three constituencies, the Monmouthshire constituency that had elected two members until 1885. The constituency was abolished for the 1918 general election, when most of its area became the Monmouth county constituency.

In 1852, the old constituency had elected members of two powerful families - the Morgans of Tredegar and the Somerset dukes of Beaufort. In 1885, the Morgan interest continued with the election of Colonel Hon. Frederick Courtenay Morgan as MP from 1885 until 1906 when he retired. His son, Courtney Morgan, afterwards Baron Tredegar attempted to succeed him, but was defeated by another local landowner Colonel Ivor Herbert of Llanarth, Monmouthshire. Herbert retained the constituency until 1917 when he departed to the House of Lords. The constituency was abolished a year later.

The constituency consisted of:

• The petty sessional divisions of:
  • Caerleon (the civil parishes of Caerleon, Kilgwrrwg, Llandegveth, Llangattock, Llanhennock, Llanthewy-vach, Llanvihangel, Llantarnam, Llanfrechfa Lower and Tredunnock)
  • Chepstow (Caerwent, Caldicot, Chapel Hill, Chepstow, Howick, Ifton, Itton, Llanfihnagel juxta Rogiet, Llnavair Discoed, Mathern, Mounton, Newchurch, Penterry, Portskewett, Rogiet, St Arvans, Shirenewton, Tintern Parva)
  • Christchurch (Bishton, Christchurch (part), Goldcliff, Kemeys Inferior, Llangstone, Llanmartin, Llanvaches, Magor, Nash, Penhow, Redwick, St Brides Netherwent, Undy, Whitson and Wilcrick)
  • Monmouth (Dixton (part), Mitchel Troy, Monmouth (part), Rockfield and Wonastow)
  • Newport (Bassaleg, Bettws, Coedkernew, Duffryn, Graig, Henllys, Llandavenny, Machen, Malpas, Marshfield, Michaelstone-y-vedw, Peterstone, Risca, Rogerstone, Rumney, St Bride's Wentloog, St Mellons and St Woollos (part))
  • Raglan (Bryngwyn, Clytha, Dingestow, Llanarth, Llandenny, Parc Grace Dieu, Penrhos, Pen-y-clawdd, Raglan and Tregare)
  • Trellech (Cwmcarvan, Llandogo, Llanishen, Llangoven, Llanfihangel Tor-y-Mynydd, Penallt, Trelleck and Wolvesnewton)
  • and Usk (Bettws Newydd, Gwehellog, Gwernesney, Kemeys Commander, Llanbadoc, Llangeview, Llangibby, Llangwm-Isaf, Llangwm-Ucha, Llanllowell, Llansoy, Llantrissant, Monkswood, Trostrey and Usk)
• The parts of the municipal boroughs of
  • Monmouth
  • and Newport outside the Monmouth Boroughs constituency
• The civil parishes of
  • Bedwas
  • and Mynyddislwyn.^[1]