Calls had circulated on social media networks for protesters to gather near parliament to prevent lawmakers from joining the session.
The government had already declared a two-week state of emergency on August 5, the day after the explosion that killed 171 people and ravaged the heart of the capital.
Under the law, the army can ban gatherings deemed threats to national security, shut down assembly points, and expand the jurisdiction of military courts over civilians.
Lebanese are furious at a political leadership that allowed a large shipment of hazardous ammonium nitrate fertiliser to languish for years in a port warehouse despite repeated safety warnings.
As he presented his government's resignation on Monday, Prime Minister Hassan Diab blamed the blast on decades of corruption and official mismanagement.
According to Lebanese law, the government can only issue a state of emergency for eight days, while the hemicycle must approve its extension for longer periods.
Protests have rocked central Beirut on successive nights, leading to scuffles with security forces who have fired tear gas and rubber bullets to disperse the crowds.
U.S. Under Secretary of State for Political Affairs David Hale will arrive in blast-hit Lebanon Thursday for a three-day visit.
It came at a time when Lebanon was dealing with a severe financial crisis along with the coronavirus pandemic.
"We hope that Brazil does not limit its assistance to Lebanon to humanitarian aid, because Lebanon is also in need for construction material including aluminum, glass, wood and concrete", Aoun said during his meeting with visiting former Brazilian President Michel Tamer.
Hale will also underscore "America's willingness to support any government that reflects the will of the people and is genuinely committed to and acting upon such a reform agenda".