[2] The town was formed around Harris's Deep Navigation Colliery, which begun coal mining excavations in 1878, after sinking started in 1872.

During the early 21st century, like many ex-mining villages in the area, Treharris underwent significant regeneration to the town/village centre.

Most, if not all of the land where Deep Navigation was situated has been landscaped and is now part of the new Parc Taff Bargoed, where many of the local football and rugby teams train and play.

[5][6] The Welsh International Climbing Centre, an indoor climbing centre and caving complex, is built on the site of the former Trelewis Drift mine and is an integral part of the Millennium park complex.

The sketch "The Worm That Turned", from the BBC series The Two Ronnies, was filmed around Treharris.

The television drama Richard Burton's A Christmas Story was filmed around Treharris in 1990.