'Fate in Lebanon'
A win for Hezbollah, which the US has listed as a so-called "terrorist" organisation, and its Maronite Christian allies from the Free Patriotic Movement, could precipitate a tilt towards Syria.
But most analysts predict the outcome is likely to be a national unity government - albeit one in which Hezbollah has a strong hand - with little change likely in government policy.
The Christian vote - divided between the two camps - looks set to tip the scale, with a handful of key battleground constituencies likely to be crucial in determining the elections outcome.
Speaking to supporters ahead of the midnight deadline to end campaigning, Saad al-Hariri, the leader of the March 14 coalition, said the vote would decide the future of Lebanon.
"All what we wish for is that that our opponents would recognise the result of the election," he said at a rally of his Future movement in Beirut on Friday.
"The decision [following the vote] ... is the decision that will determine the fate in Lebanon."
Lebanon has witnessed a period of calm in the run-up to the election, but sectarian tension brought Lebanon to the brink of civil war last year.
More than 100 people were killed in violence before an agreement led to the election of Michel Sleiman, then the army chief, as president and the formation of a national unity government.
Lebanon's complex power-sharing system divides the 128 seats in parliament equally between Christians and Muslims.
The country's president must be a Maronite Christian, the prime minister a Sunni Muslim and the speaker of parliament a Shia Muslim.
The current Sunni-led majority in parliament swept to power in 2005, amid a wave of popular discontent following the murder of Rafiq al-Hariri, a former prime minister, in a massive car bombing in Beirut.
Reaction to the bombing prompted the withdrawal of Syrian troops from Lebanon after a 29-year presence amid accusations - strongly denied by Damascus - of Syrian involvement.
It also marked the beginning of a turbulent period during which Hezbollah was thrust to the political forefront by its 34-day war with Israel in which 1,200 people died in Lebanon, most of them civilians.
Political unrest last year also saw a six-month vacancy in the presidency and sectarian clashes that killed more than 100 people after Hezbollah staged a spectacular takeover of mainly Sunni parts of Beirut.