Company Formation and Parliamentary authorisation
The company was formed in 1859 and parliamentary approval was received on 1 August for the northern section of the line from Llanidloes, Montgomeryshire to Llandovery, Carmarthenshire. Approval for the southern section from Newbridge-on-Wye to Three Cocks Junction in northern Brecknockshire was received on 3 July 1860.
The first sod was ceremonially cut on 2 September 1859, but further work on the 46.7 mile line was delayed until 1862. A formal opening ceremony was held on 23 August 1864, and the line to Three Cocks Junction was opened goods traffic on 1 September.
Parliament had authorised both the MWR and the Manchester and Milford Railway to connect Llanidloes to Aberystwyth, and so the M&MR had prioritised construction in the Llanidloes area. Eventually an agreement was reached to form the joint Llanidloes and Newtown Railway, which extended 1.5 miles (2.4 km) south to Pentrabane junction, where the MWR and M&MR's short-lived Llangurig branch diverged. The L&NR opened its line in 1859, enabling through working to and from the MWR line.
The MWR worked the line of the Hereford, Hay and Brecon Railway from 1 October 1868 until that company was taken over by the Midland Railway on 1 October 1869. The line from Builth Road to Llandovery was not built, but a connection to the Central Wales Extension Railway was completed on 1 November 1866, enabling goods trains to run to and through that station.
At Brecon, following the initial opening of three separate stations, a joint station was created at Free Street.
At Llanidloes railway station, the grand junction building that was created in anticipation of M&MR traffic which never materialised, since the Mid Wales Railway never completed their section of the Llangurig - Strata Florida - Aberystwyth line.
The Welsh Railways Through Traffic Act of 1889 went some way to formalising an arrangement to create the Mid Wales Line, to form part of a through route from South Wales to Cheshire, as an alternative to the main line route via Hereford and Shrewsbury (i.e. Newport, Abergavenny and Hereford Railway plus Shrewsbury and Hereford Railway) . The main route was made up of (North to South):Great Western Railway: Oswestry to Gobowen for the Shrewsbury and Chester Railway
Potteries, Shrewsbury and North Wales Railway: Shrewsbury to Llanymynech
Shrewsbury and Welshpool Railway: GWR and LNWR mainlines at Shrewsbury to Welshpool
Oswestry and Newtown Railway: Oswestry to Newtown
Llanidloes and Newtown Railway: Newtown to Penbontbren Junction
Mid-Wales Railway: Penbontbren Junction to Talyllyn Junction
Hereford, Hay and Brecon Railway: Three Cocks Junction to Hay-on-Wye.
Brecon and Merthyr Railway: Talyllyn Junction to Merthyr, and onwards to Cardiff
Neath and Brecon Railway: Brecon to Neath, accessing the South Wales Main Line
Swansea Vale Railway: to Swansea docks and West Wales
The links necessary to complete the route included the Oswestry, Ellesmere and Whitchurch Railway to connect to the LNWR at Crewe, and the Wrexham and Ellesmere Railway to connect to the Wrexham, Mold and Connah's Quay Railway and hence onwards to Liverpool. These links were not complete until 1896.
In practice the Mid Wales Line never received substantial use, and that almost entirely for goods traffic. As a result, the Mid-Wales Railway encountered financial problems, and the company's locomotives and rolling stock were sold. A working arrangement was signed with the Cambrian Railways (CamR) which took effect on 2 April 1888. Formal vesting of the line in the CamR followed on 24 June 1904.
Normal goods and passenger trains along the CR/MWRs route were stopped in World War I by intensive coal trains, dubbed Jellicoe Specials after the Admiral of the Fleet John Jellicoe, 1st Earl Jellicoe, from the South Wales Coalfield travelling north towards Scapa Flow for use by warships of the Royal Navy.
The whole of the CR/MWR route, and its stations, from Moat Lane Junction to Talyllyn Junction, were closed for passengers throughout by British Railways on 31 December 1962. The section between Moat Lane Junction and Llanidloes remained open for freight traffic until 1967.