Protesters gathered near the main courthouse in Tunis as police barred journalists from entering the building at the behest of the prosecutor, reporters were told.
Inside, black-robed lawyers chanted "Freedom!" and "The police state belongs in the past!", according to videos streamed live on social media.
The protest was called by the bar association which this week also decided on a nationwide strike after Sonia Dahmani and Mehdi Zagrouba were arrested when police raided its headquarters on Saturday and Monday.
Zagrouba was taken to hospital after fainting and being beaten while in custody, lawyers said.
The president of the bar, Hatem Meziou, on Tuesday called for an end to "the abuse of power" and "violence" targeting lawyers.
He called the police raids unlawful and urged President Kais Saied to intervene.
But Saied said Thursday that "the bar association is located on Tunisian soil and is not subject to (its own) territorial regime so that anyone can hide there".
He said the arrests took place "in full respect for Tunisian law, which guarantees equality and the right to a fair trial", according to a video released by the presidency on social media.
Saied, who granted himself full authority after a sweeping power grab 2021, said that "no one is above the law".
The European Union, France and the United States have all expressed concern after the two lawyers were detained.
Saied on Thursday called such criticism foreign "interference", and told the foreign ministry to "summon as soon as possible the ambassadors of a number of countries", without specifying which ones.
