The first section of the line, as far as Pontypridd, is historically part of the Taff Vale Railway, from Cardiff to Merthyr Tydfil.

In March 2007 it was announced that platforms on the branch are to be lengthened to enable 6 car trains to run, together with leasing of an additional eight Class 150s for the whole network.

On 20 July, Arriva Trains Wales announced a summer trial of extra Sunday services to Cardiff and Barry Island.

[6] On 16 July 2012 plans to electrify the line were announced by the UK Government as part of a £9.4bn package of investment of the railways in England and Wales.

[8][9] However, as part of Welsh Government's South Wales Metro this line has been taken over,[10] and is now being electrified[11] in preparation for new Class 398 tram-train rolling stock.