The Newport, Abergavenny and Hereford Railway was a railway company formed to connect the places in its name. When it sought parliamentary authorisation, it was denied the southern section, and obliged to use the Monmouthshire Railway between Pontypool and Newport.
It opened on 6 December 1853, and was part of an important chain of lines between south-east Wales and Birkenhead; mineral traffic in both directions was dominant. The London and North Western Railway hoped to exploit the line to form a network in South Wales, but that aspiration was not fully realised, and in 1860 the NA&HR merged with other railways to form the West Midland Railway, which soon amalgamated with the Great Western Railway in 1863.
In order better to serve the ironworks in the South Wales Valleys, the NA&HR built the Taff Vale Extension Line, running west from Pontypool and cutting across several of the valleys, making connections with other companies' lines, eventually at twelve locations. The line was opened in stages from 1857, and included the Crumlin Viaduct crossing the valley of the Ebbw River.
After 1945 local passenger and goods business collapsed, and somewhat later the mineral industries declined too. By 1979 only the Pontypool to Hereford main line, and some short stubs of the Taff Vale Extension Line remained in use, but the main line flourished, and continues in use as an important secondary main line.