Scores of asylum-seeker families, including babies born in Australia, face the prospect of deportation to Nauru after a High Court ruling.
The full bench of the court on Wednesday rejected a legal challenge to the federal government's offshore immigration detention regime.
It did so after considering the case of a pregnant Bangladeshi asylum seeker who was brought to Australia from Nauru for treatment for serious health complications.
She faced the prospect of being returned to the Pacific island with her one-year-old child.
In a majority decision the court said the woman's detention on Nauru was not unlawful.
It also ruled the commonwealth's role in her detention was authorised under Australian migration laws, and the government's offshore processing deal with Nauru was valid under the constitution.
"The High Court held, by majority, that the plaintiff was not entitled to the declaration sought. The conduct of the Commonwealth in signing the second MOU with Nauru was authorised by s 61 of the Constitution," the judgment said.
"The Court further held that the conduct of the Commonwealth in giving effect to the second MOU (including by entry into the Administrative Arrangements and the Transfield Contract) was authorised by s 198AHA of the Act, which is a valid law of the Commonwealth."
