The South Wales Main Line was one of the last of the major inter-city routes in Great Britain to remain un-electrified.
 The government announced in 2012 a scheme to electrify the South Wales Main Line as part of a wider scheme of electrification on the Great Western Main Line.
The line from London to Cardiff was fully electrified by Christmas 2019.

The new Hitachi Super Express trains planned for the Great Western inter-city services will now be predominantly electric units instead of the planned diesel units.
 However, a proportion of the fleet will be using dual power source electro-diesel bi-mode trains, which will enable services to operate before line electrification is complete.
The bi-mode trains will allow inter-city services to operate from London all the way to Carmarthen in the future.
The new Super Express trains will bring about an estimated 15% increased capacity during the morning peak hours.
 Electrification has cut journey times between Swansea and London by an estimated 20 minutes, although electrification will not extend west of Cardiff to Swansea, Carmarthen or Pembroke Dock, and services on the line to Brighton, Portsmouth Harbour and Taunton will continue to be operated by diesel trains, as the Bristol to Exeter Line and the Wessex Main Line will not be electrified.
The South Wales Main Line was one of the last of the major inter-city routes in Great Britain to remain un-electrified.  The government announced in 2012 a scheme to electrify the South Wales Main Line as part of a wider scheme of electrification on the Great Western Main Line. The line from London to Cardiff was fully electrified by Christmas 2019.
The new Hitachi Super Express trains planned for the Great Western inter-city services will now be predominantly electric units instead of the planned diesel units.  However, a proportion of the fleet will be using dual power source electro-diesel bi-mode trains, which will enable services to operate before line electrification is complete. The bi-mode trains will allow inter-city services to operate from London all the way to Carmarthen in the future. The new Super Express trains will bring about an estimated 15% increased capacity during the morning peak hours.  Electrification has cut journey times between Swansea and London by an estimated 20 minutes, although electrification will not extend west of Cardiff to Swansea, Carmarthen or Pembroke Dock, and services on the line to Brighton, Portsmouth Harbour and Taunton will continue to be operated by diesel trains, as the Bristol to Exeter Line and the Wessex Main Line will not be electrified.
South Wales Main Line