Helen O'Sullivan was part of a rally outside Brisbane Magistrates Court backing almost 30 people who had allegedly breached Queensland's new prohibited expression laws.
The grandmother was among a group of protesters supporting fellow flotilla member Sam Woripa Watson and dozens of others due to appear in court on Tuesday.
About 26 people faced charges under the Liberal National government's hate speech laws that outlaw phrases such as "from the river to the sea".
"We are speaking against the Crisafulli government that is attempting to silence valid criticism of the state of Israel," O'Sullivan said on a loudspeaker outside court.
"From the river to the sea is a call for democracy and freedom."
Police did not intervene when O'Sullivan addressed the crowd with the phrase and she went on to repeat it outside court.
"On behalf of all children of Palestine, I am saying from the river to the sea, free free Palestine from apartheid, from illegal occupation, from genocide," she said.
Police officers moved in to arrest O'Sullivan soon after Watson and others previously charged with prohibited expression entered the court building.
Watson said outside court he intended to contest the charge if a High Court challenge to the validity of the law was not successful.
O'Sullivan and Watson were detained by the Israeli military in May alongside nine other Australians who took part in a convoy of small boats with the stated aim of bringing humanitarian aid to the Gaza war zone.
Watson allegedly used the "river to the sea" phrase during a speech to about 300 people in Brisbane's King George Square after being returned to Australia from Israeli custody.
Queensland in March banned the phrases "from the river to the sea" and "globalise the intifada", categorising them as hate speech against Jewish people under new "fighting anti-Semitism" legislation.
The highly contested phrases are seen by some to advocate for the genocide of Jewish people from the Jordan River to the Mediterranean Sea.
The laws were a "common sense" response to the Bondi terror attack, Queensland Attorney-General Deb Frecklington said in February.
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