Prosecutors have said the case was the first of its kind in Britain.
Farayadi Sarwar Zardad, 42, was convicted on Monday of running a private army that brutalised Afghans in the Sarobi district east of Kabul which he commanded in the 1990s before he was ousted by the Taliban.
Zardad was found guilty at London's Old Bailey criminal court of conspiracy to torture people and take hostages.
The unprecedented case - Zardad's second trial after a jury failed to reach a verdict last year - was the first in Britain to involve human rights violations committed abroad and to have witnesses give evidence anonymously via a satellite link.
The court heard how Zardad's men and the commander himself committed atrocities between 1991 and 1996 when he commanded an 80-km area which included a key highway from Pakistan to the Afghan capital.
London pizza parlour
He moved to Britain in 1998 seeking asylum and was running a pizza parlour in south London when he was arrested in 2002 after his case was brought to light by a BBC journalist.
Afghan witnesses, who said they received death threats for agreeing to give evidence in Kabul where Zardad's name is still feared, recounted how his men had robbed, beaten, raped, and murdered travellers at checkpoints and a nearby prison.
Zardad belonged to Gulbuddin
Hekmatyar's (above) party
The most striking evidence concerned a certain Abdullah Shah, Zardad's "human dog" who ate victims' flesh and who was executed in April on the orders of Afghan President Hamid Karzai for murdering dozens of people.
Shah, whose reputation helped cement Zardad's position, was kept chained in a hole and would be unleashed on civilians, biting them and eating their flesh under the orders of Zardad's men, the court heard.
British police who met Shah described him as being like "Hagrid from Harry Potter, but much scarier".
The verdict was seen as a boon to human rights campaigners who have long called for countries to prosecute war criminals for actions carried out anywhere in the world.
"We believe this is the first time in any country, in international law, and certainly in English law, where offences of torture and hostage taking have been prosecuted in circumstances such as this," prosecutor James Lewis said.
In his homeland, Zardad had belonged to Hizb-i-Islami, led by Gulbuddin Hekmatyar, a mujahidin leader who became prime minister of Afghanistan during the civil war in the early 1990s.
Hekmatyar is now a fugitive allied to the Taliban which was ousted by US forces in late 2001, and his fighters are involved in an uprising in the southeast of Afghanistan.