Ffos Y Fran mine to close in November
Its operator has submitted a closure date to the Welsh Government.
The UK's biggest opencast coal mine based in Merthyr Tydfil will close later this year
The mining of Ffos-y-Fran will cease on November 30 after 15 years of extraction.
The operator, Merthyr (South Wales) Ltd, has submitted a notification to the Welsh Government confirming the closure date.
It comes after its planning permission ran out in September 2022 and its appeal for more time was refused by Merthyr Tydfil County Borough Council on climate grounds.
Around 180 people who work at the site will be made redundant.
Opencast mining at the site has proven controversial over the years, with some local residents concerned about the levels of noise and dust.
Campaigners have been fighting to get the mine closed and recently launched legal action with the support of the Good Law Project to get production halted.
But British heritage railways and traction engine owners will now have to import coal from overseas as their only source of UK coal will end.
Llyr Gruffydd MS, chair of the Senedd's Climate Change, Environment and Infrastructure Committee, called for support for those losing their jobs.
He said: "This announcement will bring clarity to an issue that has been of significant concern for the local community and environmental campaigners.
"It is important that we now look to the future.
"Ffos-y-Fran is a significant employer in the area, and we have asked the Welsh Government what plans are in place to support the workers and the local economy after the closure of the mine.
"We have also heard concerns about a significant shortfall in the funds put aside by the company to restore the land.
"The local community, which has lived with this mine for so many years, must get what it was promised.
"The committee has written to the minister on these issues, and we await a response.
"We will continue to press the Welsh Government to provide answers on support for the redundant workers as well as the fund for restoring land as we approach the closure date in November."