Syed Nazrul Islam entered the Pakistan Central Superior Service in 1949 and won. He thereafter joined the Department of Taxation as an officer. To become a professor of history at Ananda Mohan College (Mymensingh), he left the government in 1951. He then became a member of the Mymensingh neighborhood bar. Being a member of the All-Party Action Committee allowed him to actively participate in the linguistic movement.

Syed Nazrul began his political career as an Awami League activist. In 1957, he was chosen to lead the party’s district organization in Mymensingh.

From 1964 until 1972, Syed Nazrul Islam served as the senior vice president of the Awami League’s central committee. After Bangabandhu Sheikh Mujibur Rahman was imprisoned during the movement with the six-point agenda, he continued to retain the position of acting president of the Awami League (1966–1969). He was a key figure in the anti-Ayub campaign of 1969 as one of the Democratic Action Committee’s leaders. He was a representative of the Awami League at the Round Table Conference in Rawalpindi, which was organized by President Mohammad Ayub Khan (1969).

In 1970, Syed Nazrul Islam was chosen as a representative from Mymensingh in the Pakistan National Assembly. He was also chosen as the Awami League parliamentary party’s deputy leader. He was an associate of Bangabandhu during his conversation with President Yahya khan in March 1971 and played a significant part in the non-cooperation campaign (19 March 1971). After Bangabandhu’s arrest on March 25, 1971, he served as the Awami League’s interim president.

Syed Nazrul Islam led the battle for freedom as Acting President of the Mujibnagar administration, which was established on April 10, 1971, while President Sheikh Mujibur Rahman was away. He served in Bangabandhu’s first cabinet as the minister in charge of the industry ministry. He served on the committee that wrote the Bangladeshi Constitution. In 1972, he won the Awami League parliamentary party deputy leader position.

In 1973, Syed Nazrul Islam was chosen to represent Mymensingh in the Jatiya Sangsad. He was once more chosen as the Awami League’s deputy leader in the Sangsad. He served in Bangabandhu’s cabinet and was in charge of the Ministry of Industry. Nazrul Islam was appointed vice president and vice chairman of the Bangladesh Krishak Sramik Awami League after the country’s one-party presidential system was implemented in 1975. (BAKSAL).

Martial law was enacted, and Khondakar Mostaq Ahmad was elected president of the nation following the killing of Bangabandhu Sheikh Mujibur Rahman by a group of army officers on August 15, 1975. Some of Khondakar Mostaq’s previous coworkers were successful in entering his cabinet. However, the top four Awami League figures, Syed Nazrul Islam, Tajuddin Ahmed, M. Mansur Ali, and Ahm Qamaruzzaman, were detained on August 23 and detained in the Dhaka central jail when they voiced their unwillingness to join the cabinet.