Better known as HT Imam, he was being treated at Combined Military Hospital where he breathed his last around 1:15am on Thursday, said Biplab Barua, office secretary of the Awami League.
Decisions on his funeral prayers and burial will be taken later, Barua added.
Remembering the role he played during the 1971 Liberation War, President Md Abdul Hamid in a condolence message said Imam also greatly contributed to the rebuilding of the war-ravaged country.
Awami League chief Hasina and General Secretary Obaidul Quader have also mourned Imam.
A member of the ruling party’s advisory council, Imam was suffering from age-related problems coupled with kidney complications, according to an Awami League leader close to his family.
He had been advising Hasina on political affairs since 2014.
While working in the then Pakistani government, Imam defected to Bangladesh and joined the Liberation War.
He was the first cabinet secretary to the government during the war.
Born on Jan 15, 1939, he graduated from Rajshahi University in 1958 before getting his master’s degree from Dhaka University. He also had a post-graduate diploma in development administration from the London School of Economics.
He grew up in several districts as his father, a public servant, was transferred frequently. He passed matriculation exams from Dhaka Collegiate School and intermediate exams from Pabna Edward College.
Imam joined Rajshahi Government College as an economics lecturer. Later, he took a government job after clearing Pakistan Civil Service tests.
After independence, he worked as cabinet secretary until Aug 26, 1975. He then worked as a project director of the Public Administration Training and Management Project, now BPATC, from 1978 to 1984. He later worked as secretary to communication and planning.
After retirement, he became actively involved in the Awami League’s politics. He played a key role in the Awami League’s national election campaigns as co-chair of the party’s election conduction committee. Hasina is chairperson of the committee.
After returning to power, Hasina made him her adviser on public administration.
Critics consider his books on conducting the Liberation War as important documents of the war.
Imam never contested in elections. His son Tanveer Imam is the MP from Sirajganj-4 constituency.