An advocate has been given another chance to fight for key documents from the botched robodebt scheme to be made public.
Justin Warren first sought out 10 business case documents in 2017 under Freedom of Information laws but was refused access by the Department of Human Services, now known as Services Australia.
After years of legal challenges, the Administrative Appeals Tribunal decided against granting Mr Warren access to the documents in December 2022.
The advocate launched an appeal in the Federal Court last year, arguing the tribunal hearing was procedurally unfair.
His lawyers also argued the evidence put forward by Services Australia, in written submissions, was changed without any notice.
Federal Court Justices Anna Katzmann, Shaun McElwaine and Geoffrey Kennett on Friday ruled in Mr Warren's favour.
The judges found Mr Warren had been deprived of the procedural fairness he was entitled to in the tribunal hearing.
That included evidence that Services Australia brought forward without telling Mr Warren the case had been altered.
"Mr Warren was deprived of the opportunity of knowing what case Services Australia sought to make out on confidential evidence that he was not privy to," the judgment said.
The tribunal's December 2022 decision was set aside and a new tribunal hearing was ordered.
The judges also ordered Services Australia to pay Mr Warren's legal costs.
Mr Warren welcomed the legal victory as a win for government transparency.
"(Robodebt) was a deliberate, systematic process of abuse conceived in secret and executed with malice," he said in a statement.
"The only way we can prevent this from happening again is by keeping a close eye on what the government is doing at all times."
The robodebt scheme, initiated under the former coalition government in 2015, sought to recover $1.2 billion over four years from more than 860,000 welfare recipients.
But more than $750 million was wrongfully recovered from 381,000 people.
The federal government is now implementing 56 recommendations from a royal commission into the scheme.
Maurice Blackburn principal lawyer Jacinta Lewin said the Federal Court's ruling would hold government to account.
"This decision provides much needed clarity on Freedom of Information law and the use of the cabinet document exemption," she said.
"It is also a case study in perseverance ...Justin Warren's attempts to seek answers were relentlessly fought."
A Services Australia spokesman said it would consider the judges' reasons and liaise across government to determine next steps.
