Abdul Quader Molla, 64, the fourth highest ranked leader of the Jamaat-e-Islami party, is the first politician to be found guilty by the International Crimes Tribunal, a much-criticised domestic court based in Dhaka.
Before the verdict was announced, a man was burned to death as riots rocked the city.
Molla was sentenced following charges of rape, genocide and murder.
Jamaat announced a nationwide strike on Tuesday and warned it would resist at any cost a "government blueprint" to execute its leaders.
The verdict is expected to be given at around 11:30 am local
Police said a young banker was burnt to death and four people injured on Monday evening after a bus was torched by suspected Jamaat activists protesting the war crime trials of its leaders.
"He was in the bus when it was set on fire," deputy police commissioner Nisharul Arif told AFP, blaming members of Jamaat, the country's largest Islamic party for the arson.
Police clashed with protesters early on Tuesday near Old Dhaka after they smashed cars and autorickshaws. "We fired several rounds of rubber bullets to disperse them," police inspector Mizanur Rahman told AFP.
Security was tight in the capital with more than 10,000 policemen on patrol. Schools were closed and many shops and businesses shuttered. Motorways linking Dhaka with other cities were largely empty.
Protests against the war crime trials turned deadly last Thursday, leaving three people dead in the northwestern city of Bogra.
The Tribunal, a domestic body with no international oversight, was created by the country's secular government in 2010. It has been tainted by allegations it is politically motivated, targeting only senior opposition officials.
Ten other opposition figures - including the entire leadership of Jamaat and two from the main opposition Bangladesh Nationalist Party (BNP) - stand accused of war crimes.
Both Jamaat and the main opposition BNP have labelled the cases "show trials" aimed at barring the leaders from upcoming polls. International rights groups have questioned the proceedings.
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there should be a entebee type of raid to free these patriots
Very bold decision by Bangladesh. I sometimes feel that Bangladesh is able to take tough decisions, much better than India. Bangladesh has a very bright future. Bengalis in Kolkata used to say: "what Bengal thinks today, (rest of) India thinks tomorrow". May be Bangladeshis will one day start saying the same.
Keep giving rest of the sane muslims a bad name you fanatics.
It's amazing that in this article, the fact that the Tribunal was set up to prosecute war crimes committed in 1971 is omitted. The Tribunal will only prosecute Bengalis who, in 1971, collaborated with the Pakistan military, while not being members of the Pakistan military. Also, isn't the fact that Molla is widely known as "The Butcher of Mirpur" relevant?
Here. There. Everywhere. Jamaatis behave just about the same. Know what I mean....
"peaceful" is an infection that's hard to get rid of.