Hariri, a Sunni Muslim billionaire, had close ties with the United States, Western and Sunni Gulf Arab allies, and was seen as a threat to Iranian and Syrian influence in Lebanon. He led efforts to rebuild Beirut following the 1975-1990 civil war.
"The trial chamber is of the view that Syria and Hezbollah may have had motives to eliminate Hariri and his political allies, however, there is no evidence that the Hezbollah leadership had any involvement in Hariri's murder and there is no direct evidence of Syrian involvement," said Judge David Re, reading a summary of the court's decision.
Hezbollah has denied any involvement in the 14 February 2005 bombing. The reading of the verdict by the Special Tribunal for Lebanon, which began on Tuesday is expected to take several hours, comes as the country is still reeling from the aftermath of a huge explosion that killed at least 178 people earlier this month, and from an ongoing economic meltdown that has shattered their lives.
Hariri's assassination plunged Lebanon into what was then its worst crisis since the war, setting the stage for years of confrontation between rival political forces.
Even before judges began reading their 2,600 page verdict into the Hariri's killing, Lebanon's An-Nahar daily ran a headline: 'International Justice Defeats Intimidation'.
Hezbollah leader Sayyed Hassan Nasrallah said on Friday he was not concerned with the trial and that if any members of the group were convicted, it would stand by their innocence.
Hezbollah's Al Manar TV and the pro-Damascus Al Mayadeen channel did not cover the trial, which other broadcasters in Lebanon were airing live.
The verdict in The Hague may further polarise the already divided country and complicate an already tumultuous situation after the 4 August blast at Beirut port, where authorities say ammonium nitrate stored unsafely detonated, fuelling public outrage and leading to the government's resignation.
Harri's killing removed a powerful Sunni leader and allowed the further political expansion of Shi'ite power led by Hezbollah and its allies in Lebanon.