The motion for a 17-month extension, submitted by independent Christian MP Nicolas Fattouche, was passed unanimously by 98 members of the 128-seat house who attended, with rival camps blaming each other for the delay.
"The term of the mandate of the legislature will be modified on an exceptional basis to end on November 20, 2014," rather than June 20 as scheduled, it reads.
The motion to extend the normal four-year term between elections was due to "the security situation in several Lebanese regions that gives rise to political escalation and division which often take on confessional forms".
Fuad Siniora, the opposition head in parliament, explained: "We were forced to vote on this bad project to avoid a vacuum and after unrest in several regions and the serious negative development" of Hezbollah's involvement in the Syria conflict.
Also Read
The Shiite militant group has thrown its fighters into battle alongside Syrian President Bashar al-Assad's forces, while recent clashes between pro- and anti-Assad camps in Lebanon's northern city of Tripoli killed more than 30 people.
Outside the parliament building, dozens of demonstrators hurled tomatoes at a banner bearing a picture of the deputies and marked: "You have failed. Go home."
The UN special coordinator for Lebanon, Derek Plumbly, said that "while it was clearly important to ensure the continuity of institutions, it was a matter of regret that no agreement had been reached on elections".
The United Nations would "continue to encourage all parties in Lebanon to work for the expeditious conduct of parliamentary elections in line with the country's longstanding democratic tradition," he said in a statement.