Carmarthen West and South Pembrokeshire (Welsh: Gorllewin Caerfyrddin a De Sir Benfro) was a constituency of the House of Commons of the Parliament of the United Kingdom.

Its wards were split between Caerfyrddin (Carmarthen) and Mid and South Pembrokeshire.

The constituency included the whole of 22 Carmarthenshire communities (Abernant; Bronwydd; Carmarthen; Cilymaenllwyd; Cynwyl Elfed; Eglwyscummin; Henllanfallteg; Laugharne Township; Llanboidy; Llanddowror; Llangain; Llangynin; Llangynog; Llanpumsaint; Llansteffan; Llanwinio; Meidrim; Newchurch and Merthyr; Pendine; St Clears; Trelech; Whitland), the whole of 24 Pembrokeshire communities (Amroth; Angle; Carew; Cosheston; East Williamston; Hundleton; Jeffreyston; Kilgetty/Begelly; Lampeter Velfrey; Lamphey; Llanddewi Velfrey; Llawhaden; Manorbier; Martletwy; Narberth; Pembroke; Pembroke Dock; Penally; St Florence; St Mary Out Liberty; Saundersfoot; Stackpole and Castlemartin; Templeton; and Tenby), also the eastern part of the Pembrokeshire community of Uzmaston, Boulston and Slebech.

Carmarthen West and South Pembrokeshire is a marginal seat between the Labour Party and the Conservatives.

Plaid Cymru is traditionally stronger in West Carmarthenshire as well as the Tenby area where several local councillors represent the party.