As first used in the 1918 general election, the constituency was a creation of the Representation of the People Act 1918 as one of six constituencies covering the county of Monmouth. Prior to the 1918 election the county had been covered, nominally, by the county constituencies of Northern Monmouthshire, Southern Monmouthshire, and Western Monmouthshire, and the Monmouth Boroughs borough constituency. By 1918, however, administrative county boundaries were out of alignment with constituency boundaries. The new constituency boundaries took account of the new local government boundaries.