"We miss you," read large posters with a smiling picture of the popular leader.
"They feared you, so they killed you," others said.
The rally was called by the anti-Syrian coalition led by Mr Hariri's son and political heir, Saad al-Hariri, who insists those behind the killing be brought to justice.
Mr Hariri's son returned home after living for six months in exile in France and Syria in fear of his life, to issue an emotional appeal for the massive turnout as a show of Lebanese reconciliation.
"It will be a day of a renewal of faith in the unity of Lebanon," said Mr Hariri, now the head of the anti-Syrian majority in parliament.
Candlelit rallies and concerts were planned to mark the anniversary of massive bombing that killed Mr Hariri and 20 other people.
However, in a sign of continuing divisions in Lebanon, the pro-Syrian Shiite movement Hezbollah and a key Christian leader, General Michel Aoun, refused to endorse the commemoration, charging that it had been "politicised".
Tight security
Thousands of Lebanese soldiers and police were deployed in Beirut and its suburbs as people converged on Martyrs' Square, now called popularly renamed Freedom square, where Mr Hariri is buried.
Security measures have been tightened in the aftermath of demonstrations against Danish cartoons depicting Prophet Mohammed turned into a riot.
Syria to blame?
Many in Lebanon believe Syria was behind the killing of their prime minister.
An ongoing UN inquiry has implicated senior Syrian security officials and their Lebanese allies. Damascus denies any role.
Four pro-Syrian generals have been detained and charged with roles in the murder but no indictments have yet been issued.
One of Mr Hariri’s personal friends, French President Jacques Chirac, is the driving force behind several UN Security Council resolutions on Lebanon and the Hariri investigation.
"I can tell you that the international community's determination to find and punish the guilty, on the one hand, and to give Lebanon all the means for independence, security, democracy and freedom, on the other hand, has not moved at all," President Chirac told Future Television on the eve of the anniversary.
Killing turns political landscape
The February 14, 2005 assassination of Rafiq Hariri, a billionaire construction tycoon and prime minister, turned the country’s political landscape on its head.
Following his death, large protests forced Syria to end its 30 years of military presence in Lebanon and a general election was called, sweeping into power the anti-Syrian coalition for the first time since the end of the 1975-1990 civil war.
"We do not ask for a change of regime in Syria, but that it makes peace. We thank Syria for having ended the war in Lebanon but we will handle our own affairs now," Saad Hariri said in an interview with Lebanese television.
"The Syrian regime did a lot wrong in Lebanon and spared her neither insults nor threats."
The United States said on Monday that those responsible for the assassination would be brought to justice.
"The international community will not rest until we get to the bottom of who is responsible and see that those responsible are held to account for what they have done," State Department spokesman Sean McCormack told reporters.
He said Washington stands "shoulder to shoulder" with the Lebanese people in the bid to see justice is served.
Anniversary changes Valentine’s Day
Restaurants and hotels in Beirut marked Valentine's Day three days early this year so as not to clash with Mr Hariri’s commemoration.
Florists reported a rush on roses both for lovers and to be placed on Hariri's tomb.
"Every Lebanese is invited to pay homage to Rafiq Hariri on Tuesday by placing a rose at the site of the attack or at his tomb," said Druze leader Walid Jumblatt, an anti-Syrian MP.