Opposition Leader Chris Minns revealed his party would work with experts and stakeholders to develop the park on the mid-north coast between Kempsey and Coffs Harbour.
The Great Koala National Park would help protect about one fifth of NSW's endangered koala population, which are on track to become extinct by 2050.
"I don't accept that one of our most loved and iconic native species could become extinct here in just 28 years time," Mr Minns said on Thursday.
"By protecting the places these koalas live, and by working closely with all stakeholders, we can ensure we bring these incredible creatures back from the brink."
An $80 million planning process would take into account expert scientific and stakeholder advice, and include an independent economic assessment of the park's impact on local jobs and communities.
Labor would establish wildlife corridors linking Heathcote National Park, Royal National Park and Dharawal National Park to support the growth of a newly discovered koala population.
In addition, control of wildlife corridors in southern Sydney's Woronora Heights would be transferred from Sydney Water to the National Parks and Wildlife Services.
Conservation groups welcomed the multi-million dollar plan on Thursday and said protecting koala habitat is the only way to ensure the survival of the endangered species.
Koala numbers have crashed over the last two decades due to bushfires, logging and droughts, World Wide Fund for Nature Australia conservation scientist Stuart Blanch said.
"This is the kind of ambition that Australia needs to achieve the goal of protecting 30 per cent of land by 2030," Dr Blanch said.
The multi-million dollar plan was also welcomed by environmental campaigner Jeff Angel from the Total Environment Centre, who said under the government's current settings, koalas in NSW are on the road to extinction.
"Like with the climate war, the state coalition has to move beyond the koala war," he said.
NSW Premier Dominic Perrottet defended his government's own record on koala protection, saying despite brawls with the Nationals over land clearing, the party had achieved a lot for the marsupial.
"I believe we've done more than ever in any government when it comes to the expansion and enhancement of national parks," Mr Perrottet told reporters on Thursday.
"We have expanded more national parks and preserve more national parks than at any point in the history of our state."
Late last year Agriculture Minister and Nationals MP Dugald Saunders introduced a controversial bill that threatened to inflame tensions within the coalition over land clearing within koala habitat.
The bill proposed removing dual planning consent from local and state governments, making it easier for landholders to clear native forests on their properties.
The ongoing issue between the coalition partners has been dubbed "the koala wars".
Mr Saunders quietly ditched the bill days later, saying the government would undertake further consultation on the plan.
Labor's environment spokeswoman Penny Sharpe said the government had weakened environmental protections for native animals, adding that koalas in NSW were on the brink of extinction.
"Koalas can't afford another government that isn't committed to their survival," she said.
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