Lebanese Parliament Speaker Nabih Berri, right, casts his vote as parliament gathers to elect a president at the parliament building in downtown Beirut, Lebanon, Thursday, Sept. 29, 2022. AP
Deep divisions among MPs have raised fears Lebanon could be left without a president for months after Aoun's mandate runs out at the end of October, further undermining creditor confidence.
The incumbent's own election in 2016 came after a 29-month vacancy at the presidential palace as lawmakers made 45 failed attempts to reach consensus on a candidate.
Under Lebanon's longstanding confessional power-sharing system, the presidency is reserved for a Maronite Christian.
No candidate has emerged as a front-runner but among the hopefuls are Aoun's own son-in-law Gebran Bassil, a former foreign minister who is under US sanctions, and veteran politician Sleiman Frangieh.
Ahead of Thursday's session, it was not even certain enough MPs would turn up to allow a vote to go ahead but in the event quorum was achieved with 104 members of the 128-seat parliament attending, the state NNA news agency reported.
In the first round of voting, a two-thirds majority of 86 votes is required for a candidate to win, an unlikely feat in a divided legislature.
If the election goes to a second round, the required majority falls to 65, but few expect event that margin to be achieved either, fanning fears for the economy.
"If there is a political vacuum, the economic crisis would intensify and there is a clear risk of security incidents," said analyst Karim Bitar.
The Lebanese pound has lost more than 95 percent of its value on the black market since 2019 in a financial meltdown branded by the World Bank as one of the worst in modern times.
The crisis has plunged more than 80 percent of the population into poverty, as food prices have risen by 2,000 percent, the United Nations has said.
The international community has pressed Lebanese lawmakers to elect a new president in "timely" fashion to avoid plunging the country deeper into crisis
Last week, France, Saudi Arabia and the United States issued a joint statement urging MPs to "elect a president who can unite the Lebanese people".
"As Lebanon's parliament prepares to elect a new president, we stress the importance of timely elections in compliance with the constitution," the statement said.