Judge Tariq Bitar’s decision came despite fierce criticism from the Iran-backed group Hezbollah, the direction of the protracted investigation.
Bitar has been in charge since February, after his predecessor was removed by court order after legal challenges from senior government officials who were also summoned.
Hezbollah’s accusations constituted a major escalation in the rhetoric targeting Bitar, which was followed by protests in the capital, Beirut, last week by supporters of Hezbollah and its ally, the Amal movement, against the judge.
The protests turned into violence not seen in Lebanon in years: seven people were killed during five hours of clashes between supporters of the two groups and gunmen accused of allying with the “Lebanese Forces” party.
Bitar faced criticism for being responsible for the bloodshed.
But the judge went ahead on Tuesday with summoning two former ministers, one of whom is a Hezbollah ally, for questioning about the port explosion.
Bitar had issued two arrest warrants against the two former ministers, but with the resumption of parliament sessions on Tuesday during the parliamentary recess, the two ministers demanded parliamentary immunity that protected them from previous interrogation.