Chowdury Mueen-Uddin, 63, was found guilty of murdering 18 people including nine university professors, six journalists and three physicians in December 1971 with an accomplice, now living in New York.
The atrocities took place during Bangladesh's war for independence from Pakistan when an estimated 3million people were killed and 200,000 women were raped.
Convicted: Chowdury Mueen-Uddin, 63 (left), a founder of the Muslim Council of Britain, has been sentenced to death by hanging for killing 18 people during Bangladesh's war for independence. Here he is pictured showing Prince Charles around the Markfield Islamic Foundation in Leicestershire in 2003
Mr Uddin, former director of Muslim Spiritual Care in the NHS, and co-convicted Ashrafuzzaman Khan were tried in absentia after they refused to return to Bangladesh to face the trial.
There is now a warrant for their capture.
Senior judge Obaidul Hassan told a crowded court in Dhaka: ‘Justice will not be done if they are not awarded capital punishment.’
Britain refused to extradite Mr Uddin, a founder of the Muslim Council of Britain, if he were to face the death penalty when an arrest warrant was issued earlier this year.
Among the activities he has been involved in since arriving in Britain was joining the protests against Salman Rushdie’s controversial book, The Satanic Verses, and he entertained Prince Charles when the heir visited an Islamic centre in Leicester in 2003.
Absent: Mr Uddin, currently living in Britain, refused to attend the trial - as did his co-accused Mr Khan
He has previously denied the charges of being involved in the abduction and murder of intellectuals and reporters - including a BBC journalist.
Bangladesh, formerly a province of eastern Pakistan, won independence after the nine-month conflict.
Mr Uddin is accused of working with an Islamic militia called Al-Badr to violently sabotage the nation's attempts to win independence.
Current prime minister, Sheikh Hasina, formed the nation's International Crimes Tribunal (ICT) in 2010 to try war crimes suspects.
In April, the ICT made an appeal to Britain to send him to Bangaldesh to be tried alongside Mr Khan.
Sanaul Huq, the Inspector-General of Bangladesh's national police force, who is co-ordinating the ICT investigation, told The Mail on Sunday: 'They abducted an eye doctor, and then gouged his eyes out before killing him and dumping his body.
'They abducted a cardiologist and cut out his heart before killing him and dumping his body.
'They kidnapped a woman journalist, and cut her breasts off before killing her. Her decomposing body was later found with her breasts cut off.
'These victims were chosen because they were leading figures in the independence movement. Mueen-Uddin was a leading figure when it comes to killing activists. This is why we want to try him in court.
'As soon as charges are made – which I can guarantee will happen in days – we will request the British Government to hand him back to Bangladesh, and we will ask Interpol for his arrest. We will use all means, diplomatic and legal, to bring him back. If we fail, we will try him in absentia.'
Today's verdict brings the total number of war convicts up to 10 - with seven already awaiting hanging, and eight more on trial.
The evidence presented against Mr Uddin at the tribunal includes a claim by a widow, Dolly Chaudhury, who said that he was one of three men who abducted her scholar husband on December 14, 1971.
Another member of the abduction group who was caught was said to have named Mr Uddin in his confession.
Mr Uddin was working as a newspaper reporter when the war broke out.
Appeal: The International Crimes Tribunal said there cannot be justice without capital punishment for Mr Uddin who was supposedly a member of Al-Badr terrorist group which killed intellectuals for the Pakistani military
But he was also said to have secretly abducted and killed leading figures of the independence movement for the Pakistani military.
Mr Huq says Mr Mueen-Uddin fled Bangladesh shortly after independence, and went to Britain via India, Nepal and then Pakistan, from where he caught a flight to London in the early Seventies.
Over the decades, he became one of Britain's most influential Muslim leaders and is now one of the trustees of the UK's leading Islamic charity, Muslim Aid.
He was one of the chief Islamic leaders who mobilised thousands of British Muslims to protest against the publication of Salman Rushdie's controversial book, The Satanic Verses, in 1989.
Mr Mueen-Uddin has also met Prince Charles, including one occasion when the heir to the throne visited the East London Mosque in 2010.
Devastation: An estimated three million people were killed and 200,000 women were raped during the war
He has previously insisted that the war crimes charges against him were entirely politically motivated by Prime Minister Hasina's party as he was a member of the opposition.
The Bangladesh government has said, however, that the trials are needed to heal the wounds of the 42-year-old conflict, which lasted for nine months.
Towards its end, the bodies of intellectuals who were rounded up were found dumped in marshes and flood plains outside Dhaka with their hands bound.
Mr Khan, a Dhaka University student leader during the conflict, was described by prosecutors as being the ‘chief executor’ for the Al-Badr militia.
Mr Uddin did not want to comment on the sentencing today. When contacted on his mobile telephone, he hung up after saying: 'I'm not taking any calls.'