Witnesses had testified via video link from the British Embassy in Kabul in a case that was based on the UN Convention on Torture.
Lydia Aroyo, a press officer with Amnesty International, says the case demonstrates that universal jurisdiction works.
"It shows that torture is an international crime and there is no hiding place for torturers. This is important for the people of Afghanistan as well. This is the first trial of this kind under the UN torture convention of a foreign national who committed crimes in a foreign country and he was tried here in Britain," Aroyo says.
Kevin Laue is a human rights lawyer with Redress, a British-based organization that seeks reparation for torture survivors. He says the conviction of Zardad sets a precedent.
"By having tried him and found him guilty, this country shows that it's not a safe haven, it's not a place to which tortures from any parts of the world can come and live without being held accountable for their crimes. So it is a very important precedent in that regard," Laue says.
Zardad and his associates were reportedly in charge of the road from Kabul to Jalalabad in the Sarobi area from the start of 1992 until October 1996.
Beating and killing travelers, they created an atmosphere of fear and terror on the road.
Nader Nadery is a spokesman for the Afghan Independent Human Rights Commission (AIHRC). He tells RFE/RL that Zardad is fairly well known for crimes he and his men committed during the civil war in Afghanistan.
"There is some talk about him among people, especially those who traveled from Kabul toward Jalalabad during the civil war, because of his actions and behavior," Nadery says.
In a video link, one witness told the court that he was held for months and beaten so frequently that his family didn't recognize him. Another witness said one of Zardad's henchmen -- nicknamed "human dog" or "Zardad's dog " -- had bitten a man at a checkpoint because he wasn't handing out fruit fast enough.
Zardad arrived in Britain in 1998 and was running a pizzeria when he was arrested in 2002. He was found guilty of conspiracy to torture and conspiracy to take hostages. It is unclear yet whether he intends to appeal the verdict.
Zardad had belonged to the conservative Islamic party Hizb-i-Islami, led by Gulbuddin Hekmatyar, a former prime minister. Hekmatyar is now a fugitive involved in the insurgency in southern Afghanistan.
The Zardad case is significant for Afghanistan. The country is marked by widespread human rights abuses committed by former commanders and warlords during more than two decades of conflict.
The AIHRC's Nadery says the conviction and sentencing of Zardad will have a positive impact inside Afghanistan.
"The Afghan Independent Human Rights Commission welcomes such moves as positive steps toward increasing people's trust in the peace process in Afghanistan and ending impunity. The commission believes it is an important step toward ending impunity from judicial prosecution for war crimes and crimes against humanity in Afghanistan and elsewhere in the world," Nadery says.
A recent survey by the AIHRC indicated that most Afghans are directly or indirectly victims of war crimes and past human rights abuses. It also showed that most Afghan citizens believe that bringing human rights violators to justice will bolster peace and security.
Human Rights Watch recently called on the Afghan government to bring war criminals to justice. The organization has implicated several Afghan officials in past war crimes and human rights violations.