The court found in favour of OCAA on all counts and that New Hope was required to pay costs of proceedings.
Federal resources minister Keith Pitt said the High Court decision was a clear sign the Queensland government needed to overhaul its project approvals processes.
OCAA secretary Paul King said the result was a win on all counts.
"It is a better outcome than we could have hoped for," he said.
"We have won on all counts and New Hope has been ordered to pay costs to the High Court.
"The High Court's decision is, in our view, vindication that the Darling Downs is for farming - not coal mining."
A revised application to expand the mine was first rejected by the Queensland government in 2018 following a recommendation of refusal by the Land Court in 2017.
The mining company appealed the 2017 Land Court recommendation to the Supreme Court which, in 2018, found parts of the recommendation to be in error and ordered the Land Court to rehear the case, but bound by most of the original findings from 2017.
In November 2018, a reconstituted Land Court recommended the project be approved and, in 2019, the environmental approval was granted.
Further appeals to the Court of Appeal in 2019 then also found the 2017 Land Court decision to be affected by apprehended bias but did not order a fresh hearing.
The Court of Appeal decision caused doubts regarding the validity of the 2018 Land Court decision, which relied heavily on the 2017 Land Court decision that had been found to have been affected by apprehended bias.
OCAA appealed to the High Court, with leave, in 2020 arguing that it should have been afforded a fresh hearing, unconstrained by the earlier 2017 decision found to be affected by bias.
The High Court allowed the appeal and ordered a fresh hearing in the Land Court.
New Hope said it would seek an urgent meeting with the Queensland government to discuss the future of New Acland Stage 3 following the High Court decision.
The company will be asking the government for a firm commitment on the outstanding approvals for the project, which it said would generate hundreds of jobs.
New Hope CEO Reinhold Schmidt said while the High Court outcome was disappointing it had nothing to do with the strength of the Stage 3 application.
"We know, from discussions with various government departments, they have all the information they need to brief the minister on the outstanding approvals," he said.
"What we need from the government is a roadmap for how we get the project up and running because more delays equates to more job losses.
"It's no secret that the state needs these jobs and the government must make a quick decision on the future of the project so we can have some certainty.
"The project needs certainty, our employees need certainty, the community needs certainty - and the state government is in a position to provide it."
Schmidt said by acting now, the Queensland government could kickstart the rebuilding process at New Acland, allowing Stage 3 to get underway, creating more than 450 jobs and pumping $7 billion into the state economy.
"In the current environment, job creating projects such as New Acland Stage 3 are vital for the state's recovery," he said.
Pitt said the decision to send the matter back to the Land Court put hundreds of jobs in jeopardy.
"This is a classic example of the Queensland approval process allowing activists to use the courts and legal system to delay legitimate resources projects," he said
"Once again a regional area is in danger of missing out on the job and economic boost a project such as this will bring because out-of-town interstate activists know how to use the legal system to support the agenda.
"It is extremely frustrating for the many workers trying to plan their lives around the mine's future, who are now back to square one."
Member for Groom Garth Hamilton said the decision created more uncertainty for the people of Oakey.
"It's 14 years since New Hope first lodged an application to build this mine with the potential for new jobs and to secure hundreds of existing jobs in the region," Hamilton said.
"Hundreds of workers and their families have been left in limbo and it would be a tragedy for the town if New Hope fell victim to legal games and was forced to abandon the project.
"I urge the premier to work directly with New Hope to find a solution that allows the company to proceed with the New Acland coal mine."