The probe was suspended for more than a month following legal challenges from former officials charged in the case.
State-run National News Agency said an appeals court judge in Beirut rejected a case filed by a former Cabinet minister challenging Judge Tarek Bitar. That opened the door for Bitar's probe to continue.
Lebanon’s investigation into the August 2020 explosion led by Bitar was suspended for the third time in early November because of a deluge of legal challenges filed by defendants.
Several officials have refused to be questioned amid calls by some groups, including the powerful Hezbollah, to have the judge removed, accusing him of bias.
Disagreements over the judge's work between rival political groups have paralyzed the government, which has not met since Oct. 12. Hezbollah and two allied groups have demanded that Bitar be replaced.
At least 216 people died in the port explosion, caused by the detonation of hundreds of tons of ammonium nitrate stored in a warehouse for years, apparently with the knowledge of senior politicians and security officials who did nothing about it. The explosion also injured 6,000 people and destroyed parts of the city.
More than a year after the government launched a judicial investigation, nearly everything else remains unknown — from who ordered the shipment to why officials ignored repeated warnings of the danger.