"He will be hanged by neck until he is dead," chairman of the three-judge International Crimes Tribunal-2 Justice Obaidul Hassan pronounced as the convict was escorted to the dock at the crowded courtroom.
Quamruzzaman, an assistant secretary general of Jamaat, is the fourth accused who was convicted for the 1971 war crimes siding with Pakistani troops while his party was opposed to Bangladesh's independence.
Elite anti-crime Rapid Action Battalion and police enforced a sharp vigil around the tribunal complex of the special tribunal at the Old High Court complex at down town Dhaka as the verdict came while an opposition enforced nationwide shutdown for the second consecutive day.
Quamaruzzaman, 60, was brought at the court by a security convoy from the Dhaka Central Jail.
The prosecution lawyers earlier said he was a principal organiser of the so-called elite Al Badr militia forces manned by Bengali collaborators in the northern Mymensingh region which subsequently carried out atrocities and mass murders also elsewhere in the country.
The tribunal indicted him on June 4 last year on seven specific charges while it delivered the verdict after months of arguments between the prosecution and defence lawyers.
The 265-page judgement said the five of the charges including mass killings were proved in the trial.
The judgment came as the main opposition Bangladesh Nationalist Party-led opposition alliance with Jamaat being a major partner enforced for the second consecutive day a nationwide general strike to protest what they said "mass killing" of Islamists.
Officials said 21 people were killed during the May 5, 6 violence over the Hefazat-e-Islam's Dhaka siege programme.