It was the first reported death by a foreign media of a journalist in Libya.
"Ali Hassan al-Jaber has been martyred after his crew was ambushed in the region of Hawari near Benghazi," the television said, without specifying who was behind the ambush or what day it took place.
But the Doha-based channel's director general, Waddah Khanfar, said the killing followed "an unprecedented campaign mounted by the Libyan regime against Al-Jazeera and its employees."
Al-Jazeera said Jaber, a Qatari national in his 50s, was hit by three bullets and "all attempts to safe his life failed."
Correspondent Nasser al-Haddar was also wounded "after they came under sustained gunfire," it said.
Al-Jazeera, which has given blanket coverage to the Arab revolts since January, vowed it would "not stay silent in the face of this crime and will continue to try to bring the perpetrators to justice" for Jaber's killing.
On Thursday, the Brazilian newspaper Estado de Sao Paulo said one its reporters, Andrei Netto, held in Libya since March 2 had been freed by Libyan security forces.
The Estado de Sao Paulo had no information, however, about the fate of a reporter for Britain's Guardian newspaper, Ghaith Abdul-Ahad.
He was held in the same cell as Netto for several days "but the Brazilian reporter does not know where he is right now," the Brazilian paper said.