Ahmad was elected a member of the East Pakistan Provincial Assembly in 1954 as a candidate of the United Front. After the central government of Pakistan dissolved the United Front, Ahmad was jailed in 1954 along with other Bengali leaders. He was released in 1955 and elected the chief whip of the United Front parliamentary party. In 1958, with the promulgation of martial law, he was arrested by the regime of Ayub Khan. During the 6 Point Movement, Ahmad was again jailed in 1966. Following his release, Ahmad accompanied Sheikh Mujibur Rahman to the all-parties conference called by Ayub Khan in Rawalpindi in 1969. In 1970 he was elected a member of the National Assembly of Pakistan.
Sheikh Mujib and all members of his family, except his daughters, who were in West Germany at the time, were assassinated by a group of army personnel on 15 August. Ahmad immediately took control of the government, proclaiming himself President. Major General Ziaur Rahman was appointed as Chief of Army Staff of the Bangladesh Army, replacing K M Shafiullah. He praised the killers of Sheikh Mujibur Rahman calling them Shurjo Shontan. Ahmad also ordered the imprisonment of leaders Syed Nazrul Islam, Tajuddin Ahmad, A. H. M. Qamaruzzaman and Muhammad Mansur Ali. He replaced the national slogan of Joy Bangla with Bangladesh Zindabad slogan and changed the name Bangladesh Betar to 'Radio Bangladesh'. He proclaimed the Indemnity Ordinance, which granted immunity from prosecution to the assassins of Mujib. Mujib's daughters Sheikh Hasina Wazed and Sheikh Rehana were barred from returning to Bangladesh from abroad. BAKSAL and pro-Mujib political groups were dissolved. On 3 November, in what became infamously known as the "Jail Killing Day", the four imprisoned leaders Tajuddin Ahmad, Syed Nazrul Islam, A. H. M. Qamaruzzaman, and Muhammad Mansur Ali, who had refused to co-operate with Mostaq, were killed inside Dhaka Central Jail by a group of army officers on the instruction of President Khondaker Mostaq Ahmad. However, Ahmad was ousted from power on 6 November in a coup led by Khaled Mosharraf and Shafat Jamil.
Later life and legacy
Ahmad was imprisoned by Brigadier General Khaled Mosharraf and later by the Ziaur Rahman administration until 1978. Upon his release, he formed Democratic League and attempted to resuscitate his political career, but to no avail. He spent his last years in Dhaka and died on 5 March 1996. Ahmad was named in the investigation of the murder of Sheikh Mujib launched in 1996 by his daughter Sheikh Hasina, who had just won the national elections to become Prime Minister of Bangladesh. Hasina blamed Ahmad for her father's death. Due to his death, he was not charged or tried. Historians and critics assert that Ahmad was one of the key plotters of Mujib's murder. He has been criticized by Bangladeshi liberal public for legitimizing political murders by protecting Mujib's killers.