Top Awami League leaders including some elected members of both National Assembly (MNA) and Provincial Assembly (MPA) who were able to meet together in Kolkata formed into a constituent assembly in exile and drafted the Proclamation of Independence.
On the night of 25 March 1971, immediately before the military crackdown and moments before Bangabandhu Sheikh Mujibur Rahman was arrested by the Pakistan Army, he made a Declaration of Independence.
Following the announcement top AL leaders crossed over to India for safety. By 30 March 1971, most of them were able to assemble in Kolkata and drafted the Proclamation of our Independence.
Later on April 17, the official announcement declaring independence of Bangladesh by the Bangladesh government-in-exile was made.
The formal meeting of the constituent assembly was held on the day at Baidyanathtala (re-named Mujibnagar after the proclamation), a border area in the present Meherpur district, where Professor M Yusuf Ali, an MNA formally read out the Proclamation of Independence at a simple ceremony.
With this declaration the newly formed Constituent Assembly was proclaimed supreme and sovereign authority of Bangladesh.
The proclamation of Independence confirmed the Declaration of Independence made by Sheikh Mujibur Rahman on 25 March 1971.
The Proclamation declared that the independence of Bangladesh be deemed to have come into effect from 26 March 1971. It also legalised the Mujibnagar government and gave direction to all involved in the War of Liberation for establishing the chain of command.