"When the cabinet session meets for electing the president, the Loyalty to the Resistance Parliamentary bloc will elect Michel Aoun," Nasrallah said, as quoted by al Manar television broadcaster.
On Thursday, influential Sunni politician and former prime minister Saad Hariri said that he was throwing his support behind Aoun. The newly-announced backing of Hezbollah strengthens the chances of Aoun at the election scheduled for October 31.
Lebanon has been without the head of a state since 2014, when the term of then-President Michel Suleiman expired.
The president in Lebanon is always chosen from Christian candidates, according to an unwritten agreement, which also stipulates that the prime minister must always be a Sunni Muslim and the speaker of the parliament — Shiite.