Motiur Rahman Nizami, 71, could face the death penalty if convicted on Wednesday of 16 charges including genocide, rape and arson allegedly carried out during the 1971 war.
The verdict, originally scheduled for June, was postponed at the 11th hour because of a sudden deterioration in Nizami's health.
"We are finally going to get the long-awaited verdict tomorrow," prosecutor Tureen Afroz told AFP.
"We hope he will be sentenced to death for his crimes during the war."
Nizami is suspected of leading one of the war's most notorious militias, which allegedly killed top intellectuals as it became clear the new nation of Bangladesh would emerge from what was then East Pakistan.
Deputy commissioner of Dhaka police Abdul Baten told AFP security has been tightened in the capital with extra police deployed.
Authorities fear a death sentence could trigger violent protests by Nizami's Jamaat-e-Islami party, which has hundreds of thousands of activists and other supporters.
"We won't tolerate any attempt to create instability or chaos," junior home minister Asaduzzaman Khan told reporters.
Other verdicts as well as the execution of a senior Jamaat leader last year plunged the country into one of its worst crises as religious parties battled security forces, leaving around 200 people dead.
Nizami, the president of Jamaat, is already on death row after being sentenced to hang in January for trafficking a huge cache of weapons and trying to ship them to a rebel group in northeast India.
Since it was created in 2010 by the government of Prime Minister Sheikh Hasina, the war crimes court has sentenced around a dozen opposition leaders for war crimes.
Religious parties accuse the government of using the court to target opposition leaders.
But Hasina's secular government maintains the trials are needed to heal the wounds of the conflict that it says left three million people dead.
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“We won’t tolerate any attempt to create instability or chaos,” junior home minister Asaduzzaman Khan told reporters. I wish the Pakistani leadership has the same guts as of Bangladesh but the selfish opportunist leaderships in the past and present have given nothing but terrorism as an economic and power solution. Still time to follow Bangladesh if we love Pakistan, to get rid of these fanatic criminals while showing the justice via judicial system without any fear of personal consequences.