Law firm Maurice Blackburn, which took a class action on behalf of victims, was denied special leave to challenge a court win by government-owned dam operator Seqwater in Australia's highest court on Tuesday.
Rebecca Gilsenan, from Maurice Blackburn, said it was a disappointing end to the decade-long legal fight.
"This is the end of the case against Seqwater and there are no further avenues for appeal because the High Court is the highest court in Australia," Ms Gilsenan said.
"We know that this is a deeply disappointing outcome after an extraordinarily long journey for everyone affected by the floods."
Seqwater was one of three parties found in 2019 to have failed almost 7000 Brisbane and Ipswich residents during the floods.
The NSW Supreme Court found engineers in control of the Wivenhoe and Somerset dams failed, and their actions made downstream flooding even worse.
In all, about 23,000 homes and businesses went under after huge water releases to make sure the dams did not fail.
The court ruled Seqwater, the Queensland government and another state-owned dam operator SunWater exacerbated flooding by failing to properly operate Wivenhoe and Somerset dams.
The Queensland government and SunWater accepted the 2019 ruling, agreeing to pay $440 million in compensation.
But Seqwater successfully appealed in the NSW Court of Appeal, leading to the final High Court challenge.
Tuesday's ruling means Seqwater does not have to pay the $440 million the flood victims claimed against it.
Ipswich councillor and 2011 flood victim Paul Tully said the High Court decision was the final "kick in the guts" for 6800 flood victims.
Councillor Tully said "justice has not prevailed in Australia today".
"We have waited 11 long years since the flood for the class action to be finalised and now this is the final kick in the guts," he said.
"Seqwater has today broken people's hearts."
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