The Llantrisant and Taff Vale Junction Railway was a railway company that constructed a standard gauge line in South Wales, connecting Llantrisant and the Taff Vale Railway near Treforest. It ran through thinly populated country, and linked to a number of iron mines, collieries and other mineral sites. It opened in stages in 1863 and 1864. In 1865 through passenger trains from the Cowbridge Railway ran over the line, to Pontypridd, although for some time there were no passenger stations on its own network. At the Llantrisant end, it was reliant on broad gauge railway companies which were not always friendly to it. The company leased its line to the Taff Vale Railway in 1870.
In 1866 it seemed likely that coal from the Ogmore Valley would be conveyed on a new line across the L&TVJR area, and powers were obtained to build the line, but the opportunity passed and when the line was finally built, in 1886, but its potential traffic had almost vanished.
The Treferig Railway opened its line in 1883 branching off the L&TVJR to serve mineral sites in Nant Mychydd. Also short of money, it leased its line to the Taff Vale Railway in 1884.
In 1952 the passenger traffic on the line was discontinued, and as the mineral activity in the area declined, so did the use of the line. It closed completely in 1987.