The billionaire businessman, regarded as the architect of Lebanon's post-war reconstruction, was buried at the downtown Mohammad al-Amin mosque after his coffin was opened in a crush of Lebanese mourners.
Chanting "Syria out," Lebanese massed in the streets amid tight security two days after Hariri was killed in a massive bomb blast that many blame on Lebanon's political masters in Damascus.
The top US envoy to the Middle East called in Beirut for the "complete and immediate" withdrawal of Syrian troops from Lebanon and demanded a "credible" investigation into the assassination.
"Mr Hariri's death should give renewed impetus to achieving a free, independent and sovereign Lebanon," Assistant Secretary of State for Near Eastern Affairs William Burns told reporters.
"What that means is the immediate and complete implementation of UN Security Council Resolution 1559, and what that means is the complete and immediate withdrawal by Syria," he said after talks with Foreign Minister Mahmud Hammud.
The United States, while stopping short of directly holding Syria responsible, has recalled its ambassador and warned of deteriorating ties, although Damascus insists it had no role in the murder.
"Beirut weeps for its martyr. Beirut salutes Rafiq Hariri," said one banner.
Church bells rang out as the procession slowly wound its way through the streets of Beirut.
His family had called for the massive public turnout, spurning a government offer to hold a state funeral and demanding that no Lebanese officials attend, although parliament speaker Nabih Berri was seen arriving at the mosque.
French President Jacques Chirac, a close friend of the slain premier, flew in to Beirut on Wednesday after the burial to pay his condolences to the Hariri family.