On its creation in 1918 the constituency consisted of the urban districts of Bedwas and Machen, Bedwellty, Mynyddislwyn and Risca and the civil parish of Rogerstone in St Mellons Rural District.
When established in 1918, the constituency encompassed the urban districts of Bedwas and Machen, Bedwellty, Mynyddislwyn, and Risca, as well as the civil parish of Rogerstone within St Mellons Rural District.