Critics have labelled the move "disgraceful" and "unfathomable", condemning the timing of the decision, but Whitehaven says the ruling will deliver a $599 million boost to the NSW economy.

It comes one day after the company was fined $158,000 in the NSW Land and Environment Court for polluting a creek near its Maules Creek mine in 2020.

The Independent Planning Commission [IPC] panel granted the approval, which is subject to 152 conditions, following a two-day public hearing in February.

Whitehaven Coal has welcomed the decision to extend life of the mine from 2031 to 2044, forecasting it will deliver 500 skilled jobs and $317 million in direct wages to the local community.

"Big investments like Narrabri Stage 3 are about lives and livelihoods and it's no surprise the majority of submissions from the local area and wider region supported the proposal, as the IPC itself acknowledged," Whitehaven Coal CEO Paul Flynn said.

"While today is a great result for Whitehaven, it's fantastic for the Narrabri region too - last financial year Whitehaven spent nearly $50 million with around 81 suppliers based in the Narrabri LGA.

"Whitehaven notes today's approval is subject to the company meeting a range of conditions imposed by the IPC.

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"The company further notes that IPC conditioning in relation to CO2 emissions aligns with its intention to reduce CO2 emissions at the mine over time together with the implementation of emissions mitigation technology and measures."

Critics such as Boggabri farmer Sally Hunter said the decision was disgraceful, and will haunt the region for "generations to come".

"Not only was the company just yesterday fined mere chicken feed for serious pollution, but it has now been rewarded with approvals for an entirely new and destructive expansion," she said.

"It beggars belief this company can commit serious crimes and instead of being appropriately punished, it is given more land to destroy, more water to drain, more lives to upend."

Independent NSW MP Justin Field has slammed the move as "unfathomable" in the context of the country's "catastrophic climate driven events" over the past month.

"While the IPC made the decision, they have been clear they believe this approval is consistent with the NSW Coalition Government's planning, mining and climate policies," he said.

"The fact new coal mining can be approved out to 2044 under existing policy makes a mockery of the Government's 50 per cent by 2030 and net zero by 2050 climate targets."

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