Mobarak Hossain was born on 10 January 1950 in the village of Nayadil near Akhaura, in the district of Brahmanbaria, Bangladesh. During the period of the charges against him, he was a member of the Islamist political party Jamaat-e-Islami and commander in the Razakars paramilitary group. This group, founded and led by the Pakistani army in 1971 to counter pro-liberation independent movements, was composed of about 4’000 volunteers. Most of the members were from the eastern part of Pakistan (now Bangladesh), and fought under the command of the Pakistan army during the Bangladesh liberation war from March to December 1971.
On 22 August 1971, Hossain and his accomplices convened a meeting in a house in the village of Tanmandail Akhaura, reportedly attended by 130 villagers. Hossain wanted to know if some of their relatives had joined the Liberation War. As part of their plan, Hossain and his accomplices removed the villagers and took them by boat to a camp of the Pakistani army near Ganga Sagar, for questioning.
On 23 August 1971, Hossain and his accomplices selected 26 persons among the villagers and seven other people from the village of Jangail and locked them in a local prison. The next day, the Pakistani army and Razakars took them to the west bank of the river Ganga Sagar, forced them to dig a ditch, then slaughtered and buried them there.
During the war, Hossain and other supporters of the Pakistan army took control of the Hindu temple Anandamoyee Kalibari, before renaming it Razakar Manjil and looting valuables therein, as well as damaging idols.
On 24 October 1971, Hossain removed the schoolboy Ashu Ranjan Dev, a member of the armed pro-liberation group Mukti Bahini. from the village of Shimrayl. He locked him up and tortured him in the Hindu temple renamed Razakar Manjil, before shooting him four days later.
On 11 November 1971, Hossain and his accomplices allegedly abducted Abdul Khaleque, a member of the armed pro-liberation group Ansar, from the village of Satian. They took him to the Razakar camp of Suhilpur and allegedly tortured him there. Hossain also shot him and charged him with the bayonet to make sure he was dead.
On 24 and 25 November 1971, a group of Razakars led by Hossain abducted Khadem Hossain Khan, an informer for Mukti Bahini, and brutally tortured him.
On 28 and 29 November 1971, Hossain, accompanied by the Pakistani army, abducted Abdul Malek of Kharampur and Mohammad Siraj of Amirpara and killed them on 6 December 1971.
After the war, Hossain remained a member of the Jamaat-e-Islami before joining the Awami League, the leading political power in Bangladesh.
On 3 May 2009, Khodeza Begum, daughter of Abdul Khaleque, filed a complaint against Hossain to the Brahmanbaria police. Hossain was then brought before the High Court, where he was granted bail for a period of six months.