Mani was the founding chairman of the Jubo League. Later he served as general secretary of the then East PakistanChhatra League from 1960 to 1964. His contribution to spearhead the historic student movement against autocratic ruler Ayub Khan’s military regime produced an immense effect. He played a pivotal role during the six-point movement in 1966. He was a student leader and general secretary of Student League. In the first week of April 1971 he along with three other Awami League leaders escaped to Kolkata. The leaders were Tofael Ahmed, Abdur Razzak and Shirazul Alam Khan. They organized the Mukti Bahini in India to liberate Bangladesh. Mani and P. N. Banerji, then joint director of Research and Analysis Wing, set up the Mujib Bahini as a counterbalance to former East Pakistan army officers in the Mukti Bahini. Members of the Mujib Bahini would go on to form the Jatiya Rakkhi Bahini. He took part in the war of liberation in 1971 as the commander of the Bangladesh Liberation Front. He initially supported the formation of a revolutionary council instead of an interim government which was against the wishes of Tajuddin Ahmed. He eventually had to give up on that and the interim government was formed. He was considered part of the inner circle of President Mujibur and was seen as loyal to Mujibur. This was the reason given for his assassination. Mani was the author of several novels, one of which was later made into a film Obanchita.
Journalism
Mani was the founder of the daily newspaper "Dainik Banglar Bani".
Death
Mani, along with his wife Arzu Moni, was killed during the Assassination of Sheikh Mujibur Rahman in a military coup on August 15, 1975. He lived two kilometers away from Mujibur in Dhanmondi. The attack on his house was witnessed by Mahfuz Anam, who is the editor as well as the publisher of The Daily Star, whose house was on the opposite side of the lake from Mani's house. His two sons - Fazle Noor Taposh, now the mayor of Dhaka South City Corporation, and Sheikh Fazle Shams Parash, an academician by profession - survived the attack, as they were hiding under a bed. His wife, who was thought to be pregnant, was also killed. Taposh was three years and eight months old then, while Parash was around five years. Taposh was elected to the Jatiya Sangsad in the 2008 Bangladeshi general election from the Dhaka-12 constituency. He was elected Mayor of DSCC in the 2020 Dhaka South City Corporation election. Parash currently holds the position of chairman of the Jubo League.
Mani was given lucrative positions in the Government formed by Sheikh Mujibur. When private trade with India was banned to slow inflation, Fazlul Haque actively engaged in it with Mujibur's blessings. This was seen as an attempt by Mujibur to form a dynasty.
