Ayuk Tabe, a charismatic leader widely deemed as a moderate in the separatist movement, was convicted with nine others of charges including "terrorism and secession", the state's lawyer, Martin Luther Achet, told AFP. They were given life terms.
The sentences were confirmed by a lawyer for the separatists, Joseph Fru, who added the 10 had also been fined 250 billion CFA francs ($422 million, 381 million euros).
Fru condemned what he called a "parody of justice" and said the defendants refused to recognise the right of the military tribunal in Yaounde to try them. Their lawyers have yet to say whether they will file an appeal.
Ayuk Tabe, a 54-year-old computer engineer by training, is the first self-proclaimed president of "Ambazonia" -- a breakaway state declared in October 2017 in two English-speaking regions of the central African country.
The government responded with a military crackdown.
Attacks by both sides have left 1,850 dead, according to the International Crisis Group (ICG) think tank, while the UN says 530,000 people have fled their homes.
- Colonial legacy -
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English-speakers account for about a fifth of Cameroon's population of 24 million, who are majority French-speaking.
Anglophones are mainly concentrated in two western areas, the Northwest Region and the Southwest Region, that were incorporated into the French-speaking state after the colonial era in Africa wound down six decades ago.
Anglophones have chafed for years at perceived discrimination in education, law and economic opportunities at the hands of the francophone majority.
Ayuk Tabe is part of the political branch of the separatist group that supports dialogue with 86-year-old President Paul Biya, who has been in power for 36 years.
But the influence of moderates waned in 2017 as Biya rejected demands for autonomy and radicals in the movement gained influence.
- 'Crisis to worsen' -
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In January 2018, Ayuk Tabe was arrested with 46 other separatists in the Nigerian capital Abuja.
They were then handed over to Cameroon, and the trial of Ayuk Tabe and the nine others began in late December. In March this year, the extradition was ruled illegal by a Nigerian court.
In late May, Ayuk Tabe said he was willing to take part in talks with the government, provided this took place abroad and the government released all people who had been detained since the start of the anglophone crisis.
But Tuesday's sentencing could crush any chance of dialogue, analysts said.
Maximilienne Ngo Mbe, head of a group called the Network of Human Rights Defenders in Central Africa (Redhac), said, "You can't develop dialogue and hand out life sentences at the same time.
"This will increase violence in these regions," she told AFP.
A specialist at the ICG said the move "risks worsening the security situation in the anglophone zone in the coming weeks."
"It could radicalise part of the separatists who had been seeing a sign of hope in the fact that the leaders had not yet been sentenced."
Cameroon's main opposition party, the Social Democratic Front (SDF), which is opposed to anglophone secession, also said the sentence worsened the breakaway crisis.
"Ayuk Tabe has much clout among anglophones. His sentencing will make the resolution of this crisis more complicated," its spokesman, Denis Nkenlemo, told AFP.
"This decision is an act of provocation which once more proves that the government isn't ready for dialogue... and is driving us straight into the wall."
- 'Torture' -
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Human Rights Watch (HRW), which says it has catalogued a litany of abuse in the troubled anglophone regions, said on Tuesday that authorities detained and tortured more than 100 prisoners, among them separatists, after a jail riot in Yaounde last month.
They were held incommunicado, beaten by gendarmes and guards and interrogated at gunpoint, it said, citing interviews with 14 detainees and several lawyers.
The unrest has crippled the economy of the Northwest and Southwest Regions and had a knock-on effect across the country.
More than one in six people in Cameroon -- 4.3 million -- need humanitarian aid, an increase of 30 percent from 2018, according to UN aid officials.