Indigenous communities could ask the High Court to rule on the fundamental question of sovereignty, after the discovery of a landmark legal rule which upends the belief that the court lacks power to decide on the matter.

Research by Melbourne Law School's Olivia Barr has found a 1935 legal rule she says means there is an 'open door' for the High Court to get involved in questions of Indigenous sovereignty.

The issue dates back to a 1970s case, Coe v Commonwealth, in which four High Court judges split two-two on the procedural question of whether the court should allow a trial on sovereignty.

The case did not go to trial because the vote was a stalemate, Associate Professor Barr said, and everyone accepted the outcome and the assumption that the High Court lacked jurisdiction.

But Assoc Prof Barr has uncovered a long-forgotten legal rule in Tasmania v Victoria (1935) that split-court decisions do not create a precedent.

'This means it is as if the Coe case never happened, so it is open to the High Court to agree to hear any case on Aboriginal sovereignty that is put forward,' she said.

Australia is the only Commonwealth country that has not signed a national treaty with its Indigenous peoples.

A treaty acknowledges the 'sovereignty' of original inhabitants, that is, their authority and power to make decisions about how best to govern aspects of their lives.

The next practical step would be for Indigenous communities and leaders to decide if a test case was a good idea, and whether the risk is justified.

'It's high risk,' Assoc Prof Barr said.

'It could lead to massive legal change, it could lead to massive legal regression, or it could lead to the status quo.'

University of Melbourne deputy vice-chancellor (Indigenous) Barry Judd said given the experience of heightened racism in the aftermath of the Voice referendum, Indigenous leaders and organisations would likely open up private discussions about what this meant.

'I think there'll be a time of deep thinking and consideration about whether it's the right time to put our heads up, or whether we might hold and think about it for longer,' he said.

The research needed to be considered in the context of the High Court's 1992 Mabo decision, which recognised that terra nullius was a myth and recognied that Indigenous people held land rights, he said.

'This research potentially gives the Australian legal system, through the High Court, an opportunity to revisit history and to revisit those questions of truth which were partially answered by Mabo, but not fully.'

Professor Judd said it raised the question of Australians taking responsibility for historical lies and 'the untruths we've lived by' since 1788.

The consequences of the research should not be feared, because if sovereignty were found to exist, this would not change the world and the sky would not fall in, he said.

'It would simply bring Australia into line with just about every other like contemporary society that was a part of the former British Empire,' he said.

Assoc Prof Barr said High Court recognition of Indigenous sovereignty would be a massive change with potentially massive benefits, leading to wider treaty-making.

'But if it's a 'no' or a status quo result, then that will be devastating, in the way that the Voice referendum result was,' she said.

'So Aboriginal and Torres Strait Islander communities need to have conversations, because it's not without risk.'

Assoc Prof Barr's research is published in the University of New South Wales Law Journal on Thursday.