Ahmed Abu Khatallah was accused of orchestrating the September 11, 2012 attack that killed Christopher Stevens, the US ambassador to Libya, and three other Americans.
On Tuesday, he was acquitted of murder but convicted on lesser terrorism-related charges.
Al Jazeera's Shihab Rattansi, reporting from Washington, DC, said Khatallah had overall been charged with 18 counts but was cleared of all but four of those, including "providing material support for terrorism".
Yet, he still faces 45 years in prison if he is given the maximum sentence for each of those four convictions, Rattansi noted.
"The prosecution had presented him as a ringleader for the attack, the defence though had said he was simply a bystander who appeared on the scene ... after the attack had taken place," said Rattansi, adding that this was a point that the prosecution "did have to concede".
"The defence also tried to poke holes in the prosecution's argument by saying that its star witness was paid $7m for his testimony," he added.
"In addition, they raised questions about the manner which Khatallah was interrogated - he was seized and then kept on a boat at sea for two weeks and interrogated without a lawyer, according to the defence."
Political storm
Khatallah has been awaiting trial since 2014 when he was captured by a team of US military and FBI officials in Libya and transported on a 13-day journey to the US aboard a navy vessel.
Before his capture, he was part of a revolutionary gang aimed at overthrowing Muammar Qadaffy
...a proud Arab institution for 42 years, now among the dear departed, though not the dearest...
's government.
Stevens was killed in the attack along with Sean Patrick Smith, a state department information management officer.
Nearly eight hours later, at a CIA complex nearby, two more Americans, contract security officers, Tyrone Woods and Glen Doherty, died in a mortar attack.
The Benghazi attack stirred up a political storm in the US, where Republicans repeatedly accused
Perennial Presidential Campaigner Hillary Crooked HillaryClinton
... former first lady, former secretary of state, former presidential candidate, Conqueror of Benghazi, Heroine of Tuzla, formerly described by her supporters as
the smartest woman in the world,usually described by the rest of us as The Thing That Wouldn't Go Away...
, the then-secretary of state, of failing to adequately protect the diplomatic compound.