Louai Al-Sakka, a Syrian, was jailed for organising and financing the truck bombings of two synagogues, the British consulate and an HSBC bank branch.
Six more people received life sentences while dozens of others received lighter sentences for the November 2003 attacks.
A Turkish cell in the al-Qaeda network claimed responsibility for the attacks, which wounded more than 600.
Güncelleme Tarihi: 20 Eylül 2018, 18:16
Sakka said in court before the verdict: "We are close to victory. The time for jihad has come, but don't worry about me. I will get out, then I will once again join your jihad."
A total of 74 people, nearly all Turks, were on trial for the bombings.
Nine appeared in court on Friday and security was tight around the courthouse, with armed security officers on roof-tops and armoured personnel carriers stationed outside.
Security sources said Sakka was a bomb-making expert and an alleged associate of Abu Musab al-Zarqawi, the former al-Qaeda leader in Iraq.
He was the senior leader in Osama bin Laden's al-Qaeda network in Turkey, security sources said.
He was accused of giving the bombers more than $150,000 to carry out the attacks in Istanbul.
Sakka, who cracked jokes with his co-defendants during the trial, had pleaded not guilty.
He was arrested in the southern Turkish resort of Antalya in 2005 after a police investigation into a plan to ram a bomb-laden boat into an Israeli cruise ship carrying tourists to Antalya.
He has yet to face trial for his alleged role in the cruise liner plot, Selahattin Karahan, his defence lawyer, said.