The lawmaker, Antoine Ghanem of the Christian Phalange party, was killed by the blast in a Christian district of the Lebanese capital. At least 19 other people were wounded by the bomb in the busy commercial and residential area of Sin el-Fil.
Several cars were set ablaze and rescue workers carried bodies from the scene in eastern Beirut.
Syria, the immediate suspect, rushed to condemn the assassination and deny its involvement in the blast.
"This criminal act was aimed at undermining efforts made by Syria and others to achieve a Lebanese national accord," Damascus' state-run news agency SANA quoted an official Syrian official as saying.
Ghanem, 64, was a member of the anti-Syrian governing coalition which has been locked in a power struggle since November with factions backed by Damascus.
Scene of attack (Photo: Reuters)
Parliament is due to convene on September 25 to elect a successor to pro-Syrian President Emile Lahoud. But political sources say resumed contacts between the rival leaders are unlikely to bear fruit in time for the vote to go ahead then.
Pierre Gemayel, the industry member and lawmaker who was assassinated in November last year, was a member of the same party as Ghanem.
Eight anti-Syrian figures have been killed in Lebanon since 2005 in a series of assassinations that started with the February 14, 2005 killing of former Prime Minister Rafik Hariri.
In June this year, anti-Syrian lawmaker Walid Eido and nine other people died in a car bomb attack.
Hariri's family says Syria was behind the killing of the former prime minister and later attacks, but Damascus denies this.
Roee Nahmias contributed to this report