Hezbollah and Amal - dubbed the "Shia duo" by local news media - are predicted to have won 29 seats in Lebanon's 128-seat parliament during Sunday's vote, according to unofficial tallies cited by politicians and local media reports.
More than 11 seats are predicted to have been won by other political parties aligned with the duo.
The long-awaited elections were marked by a voter turnout of just under 50 percent, down from 54 percent in the last legislative election in 2009, Nouhad Machnouk, Lebanon's interior minister, said on Monday.
Hassan Nasrallah, Hezbollah's leader, declared the outcome a "national achievement" in a televised speech on Monday.
Sunday's elections were Lebanon's first in nearly a decade of turbulent politics.
Since 2009, the Lebanese have watched their government collapse twice - in 2011 and 2013 - the presidency sit vacant for 29 months - from 2014 to 2016 - and their parliament extend its mandate several times.