As part of the commemoration, a group of supporters retraced the steps of the slain politician to the spot where a massive car bomb explosion killed Hariri and 22 others in 2005, The Daily Star of Beirut reported.
Hariri's assassination sparked mass demonstrations against Syria's presence in Lebanon that led to the withdrawal of Syrian troops from the country.
In June, a special tribunal indicted four Hezbollah members for involvement in the killings.
Hezbollah denied any of its members took part in the assassination and refused to hand over the suspects.
In addition to the Nejmeh Square gathering, wreaths were placed at Hariri's tomb by a delegation from the Progressive Socialist Party.