Al-Hariri, also a prominent businessman, was killed along with 22 others in a car bomb blast on Beirut's Corniche on February 14, 2005.
The killings were widely blamed on Syria, Lebanon's eastward neighbour, which at the time had troops and security officers stationed on Lebanese soil.
Army troops were deployed across Beirut in the run up to the rally, to avoid any outbreak of violence.
The commemoration of al-Hariri's death comes as Lebanon country prepares for legislative elections on June 7.
Parties from the March 14 bloc, which is backed by Washington, will be ranged against an alliance led by Hezbollah, a Lebanese political party and armed group supported by Syria and Iran.
"The upcoming elections on June 7 are a defining moment in Lebanon’s democracy; we look forward to elections in a democratic atmosphere, in compliance with the law, under Arab and international monitoring as required by the current state of affairs," Saad al-Hariri, the leader of the parliamentary majority and son of Rafiq, said in a speech at the rally.
"I call upon all the Lebanese parties to rise above differences and adopt constructive dialogue; to maintain our co-living and steer Lebanon away from any form of violence."
The turnout to the rally is seen by many analysts as an indicator of voters' mood before the elections.
"Their ability to rally people will be carried over at the ballot box," Osama Safa, head of the Lebanese Centre for Policy Studies, said.
The United Nations tribunal to try al-Hariri's alleged killers, which is due to start on March 1, will also try those presumed responsible for a series of other attacks on Lebanese leaders and journalists.
Seven suspects have been arrested in connection with al-Hariri's death, including four Lebanese generals.
Senior Syrian officials have also been implicated in the UN investigation but Damascus has denied any connection with al-Hariri's death.
Thousands of people staged demonstrations in the wake of al-Hariri's killing, calling for Syria to respect Lebanon's sovereignty.
Syria eventually pulled its troops out of Lebanon in April 2005, ending a 29-year presence in the country.