Following the failure of political negotiations, the Pakistan Army launched a brutal crackdown in Dhaka on the night of 25 March 1971 under Operation Searchlight, sparking widespread resistance across East Pakistan. As Bengali soldiers began organizing in early April, retired Colonel Mohammad Ataul Gani Osmani, known as 'Papa Tiger', was chosen to lead the emerging Mukti Bahini. Osmani, who had retired from the Pakistan Army in 1967, had previously joined politics and was elected to the National Assembly as an Awami League candidate in 1970.

During the non-cooperation movement, Osmani played a key role in mobilizing retired Bengali officers and secretly contacting serving ones to prepare for possible armed resistance. On 4 April 1971, at a secret meeting in Teliapara, senior officers including Majors Ziaur Rahman, K.M. Shafiullah, and Khaled Mosharraf unanimously selected Osmani as Commander-in-Chief of the Liberation Forces. The meeting also decided to divide Bangladesh into four military zones, later expanded to eleven.

On 10 April, the Mujibnagar Government formally appointed Osmani as Commander-in-Chief. Historians cited his seniority, wartime experience, and political legitimacy as key reasons for his selection. Under his leadership, the Mukti Bahini was organized into regular and irregular forces that fought until Bangladesh’s independence.