Turnout was 49.2 percent, down from 54 percent the last time legislative elections were held nine years ago.
The United States and Israel, which have designated Hezbollah as a terrorist organization, are on increased alert.
The Shia militia-cum-political bloc's gains came at the expense of the Sunni prime minister, Saad Hariri, whose authority was weakened by a relatively poor showing in stronghold areas. Talks over Cabinet posts are expected to take time.
Interior Minister Nohad Machnouk announced the turnout figure at a news conference shortly after midnight and appeared to blame it on the new electoral law agreed past year.
The staunchly anti-Hezbollah Lebanese Forces, a Christian party, appears to have emerged as a big victor, almost doubling its MPs to 15 from eight, according to the unofficial indications.
That's nearly 67 out of 128 parliamentary seats.
Sunday's results will still permit Hariri to form a government, but he will be compelled to make a number of concessions to Hezbollah - historically, his avowed enemy - in the process, Ghaddar said.
Amal Movement and Hezbollah won 26 Shiite seats out of 27, plus four non-Shiite seats.
Hezbollah is a substantial political party in Lebanon, and after the election controls about 10% of parliament.
"Today, we have in front of us a new stage, we have in front of us many challenges".
March 14 - an anti-Syrian, pro-Western and Saudi-backed bloc - and March 8 - a pro-Syrian, Hezbollah-led bloc - emerged following the assassination of Rafik Hariri in February 2005 and the ensuing protests in Beirut.
On the other hand, the Lebanese Forces party (LF) was the biggest victor of the elections, as its parliamentary bloc now consists of at least 14 deputies, compared to five deputies in the outgoing parliament.
The elections were the first since war broke out in Syria in 2011, sending more than 1 million refugees fleeing into Lebanon, a small country with a population estimated at around 4.5 million.
Nader was referring to Najib Mikati, a former prime minister and leader of the Majd Movement, and Faisal Karami, the leader of the Arab Liberation Party (ALP).
Lebanese Prime Minister Saad Hariri speaks during a press conference in Beirut, Lebanon, May 7, 2018.
An anti-Hezbollah alliance led by Hariri and backed by Saudi Arabia won a majority in parliament in 2009.
Since the premiership goes to a Sunni it is expected that he will stay on as premier of a government that will need to be of national unity to safeguard stability in Lebanon following tensions in the region between the Saudis and Iranians. "We made hope possible", he said.
The divisions and open hostility were on display Sunday among Hezbollah supporters and opponents of the Shiite militants. He led the Lebanese Forces militia in the last years of the civil war, during which he was an adversary of Aoun.
Lebanon's distinctive model of sectarian-driven, power-sharing politics imply rival factions usually find yourself in the identical authorities, as is the case now the place Hezbollah is represented in Hariri's cupboard.
The highly-armed, Iranian-backed group Hezbollah has gained influence from its involvement in Syria since 2012.
Ghaddar emphasized that a critical factor enabling Hezbollah's election victory was the strikingly low turnout.
Gibran Bassil, who serves as foreign minister and heads Aoun's party, told reporters on Monday that their bloc could end up having 30 seats.
"The make-up of the brand new legislative chamber represents a assure and an incredible energy to guard this strategic alternative and to guard the golden equation - the military, the individuals and the resistance", Nasrallah stated.