An "opt-in" class action, currently the legal norm, was favoured by Southern Response. In this case, people would have to consciously "opt-in" to the class action.
Meanwhile, lawyers for the class action had argued it should proceed on an "opt-out" basis - where all policyholders would be included.
The Court of Appeal agreed last year that the class action could be "opt-out", which Southern Response appealed at the Supreme Court.
Today, that appeal was dismissed.
Grant Cameron, of GCA Lawyers, was representing the class action and said today's decision was "very significant" and would help ensure that "people get access to justice".
He said today's decision in the Supreme Court was the right one.
"Instead of having 10 per cent [of a potential class] being paid out and recover what they are entitled to, everybody should be entitled to recover - in this case, the minister Megan Woods suggested the liability could be about $500m," he said.
"On an opt-in basis – which is what the government was arguing for – they could settle with the 10 per cent who came forward for $50m and keep $450m dollars."
Southern Response said in a statement it had received the Supreme Court decision in the Ross class action and would be taking some time to consider the Court's findings.
"Southern Response will not be making further public comment until it has had an opportunity to fully review the decision."