"The court has ruled, and in the name of the family of the late prime minister Rafik Hariri and on behalf of the families of the martyrs and victims, we accept the court's ruling," he said outside the court.
"Today, we have all discovered the truth," added Hariri, who attended the heavily secured court for the judgement.
The UN-backed Special Tribunal for Lebanon on Tuesday found Salim Ayyash, a member of the Shiite movement Hizbollah, guilty over Hariri's murder, but cleared three other suspects after a years-long trial.
Ayyash, 56, was convicted in absentia by the Netherlands-based court over a huge suicide bombing in Beirut that killed the Sunni billionaire politician and 21 other people.
Judges said there was not enough evidence to convict Assad Sabra, 43, Hussein Oneissi, 46, and Hassan Habib Merhi, 54, over the blast, which changed the face of the Middle East.
The judges also said there was no evidence to directly link Syria — the former military overlord in Lebanon — or Hizbollah's leadership to the attack.
Hariri on Tuesday said the verdict demonstrated the court’s objectivity and "high credibility”, as only one of four suspects was found guilty, when court critics, including Hizbollah, had expected a wholesale guilty sentence from what they have called a "politicised” court.
Even though the court did not link Hizbollah’s leadership to the attack, Hariri said he still believed the Iran-backed movement was responsible.
"Today, the party that should make sacrifices is Hizbollah,” he said.
"It is clear that the network responsible is from its ranks,” he added, saying that the perpetrators thought they could dodge justice and punishment because of Hizbollah’s protection.
"We will not rest until the punishment is carried out,” Hariri said.
"The Lebanese, as of today, will not accept for their country to be a haven for murderers.