The tribunal sentenced Sakhawat Hossain, a former member of Parliament with the Jamaat-e-Islami party, to death.
He and one other defendant were present in the court, while the six others were tried in absentia.
They must remain in prison until their deaths, a harsher punishment than life in prison, which spans 30 years in Bangladesh.
Hossain was a main committee member of Islami Chhatra Sangha, the student wing of Jamaat-e-Islami at the time of war, and was also accused of being a local commander of a group that allegedly aided Pakistani soldiers.
He left Jamaat-e-Islami and joined the Bangladesh Nationalist Party headed by former Prime Minister Khaleda Zia.
In recent years, he has been involved with the Jatiya Party headed by former military dictator H.M. Ershad.
His lawyers said that they would appeal against the court’s decision.
Bangladesh claims that Pakistani soldiers, aided by local collaborators, killed 3 million people and raped 200,000 women during the war.
Prime Minister Sheikh Hasina initiated the prosecution of suspected war criminals in 2010 by forming the tribunal.
More than 20 people have already been convicted, and five men, mostly top leaders of Jamaat-e-Islami, have been executed.
Jamaat-e-Islami, the country’s largest Islamist party, openly campaigned against Bangladesh’s independence in 1971 and reportedly formed militia groups to help the Pakistani army fight the uprising.
It said the tribunal is politically motivated, a charge the government denies.