He entered the civil service of Pakistan in 1949 but resigned in 1951 to work as a professor of history at the Ananda Mohan College in Mymensingh, where he also practised law.

[3] Nazrul Islam's political career began when he joined the Awami Muslim League and participated in the Language Movement in 1952, for which he was arrested by police.

Following the arrest of Mujib on 25 March 1971 by Pakistani forces, Syed escaped to Mujibnagar with other party leaders and proclaimed the independence of Bangladesh.

Syed played a key role in leading the nationalist cause, co-ordinating the Mukti Bahini guerrilla force and winning support from India and other nations.

When Mujib banned other political parties and assumed sweeping powers as president in 1975, Syed was appointed vice-chairman of the BAKSAL, the renamed Awami League.