The High Court decision on Monday is another blow to the legal challenge brought by Save the Children Australia against the government to compel it to return the mothers and children.
The Federal Court ruled in June the government did not have control over their detainment, with the advocacy group seeking special leave to appeal in the High Court.
Save the Children's Mat Tinkler said it continues to advocate for children overlooked by government. (Diego Fedele/AAP PHOTOS)
The group described Monday's ruling refusing that application as "marking the end of a lengthy legal battle with the federal government".
Save the Children Australia's CEO Mat Tinkler said government still has a responsibility to repatriate citizens even if the court does not see it that way.
"We respect the decision of the High Court but remain deeply disappointed at the outcome. These innocent Australian children, and their mothers, should be brought home after five long years trapped in the camps," he said on Monday.
"We will continue to advocate for the rights of these vulnerable children, who have been overlooked by their own government."
There are 34 Australians being held in detention camps in northern Syria, run by the Autonomous Administration of North East Syria (AANES) and its defence arm, the Syrian Democratic Forces.
The Roj and Al Hol camps in Syria house about 6000 foreign children of IS fighters displaced five years ago following the collapse of the militant group in 2017.
Conditions in the camps are dire with food and water lacking amid overcrowding and widespread violence and insecurity.
Four women and 13 children were returned by the Albanese government in October 2022 and the Morrison government repatriated a group in 2019.
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