Nurul Islam fell ill on his way home from an event at the Jatiya Press Club after Maghrib prayers on Saturday and was admitted to the Labaid Hospital in Dhanmondi.
He was then transferred to the ICU after doctors discovered kidney issues and a heart blockage.
Nurul Islam died at 11:30 am on Monday, said Hifazat leader Maulana Jubayer Ahmed.
Doctors had initially wanted to operate but were dissuaded because of his age and later decided to continue the treatment in the ICU, Ahmed said.
Nurul Islam Jihadi took up the post of secretary general on Dec 23 last year after the death of Nur Hossain Kasemi.
Junaid Babunagari had been the Hifazat amir at the time. Muhibullah Babunagari has been fulfilling the duties of amir since Junaid’s death on Aug 19.
Nurul Islam Jihadi hailed from Chattogram, said Maulana Jubayer Ahmed. It has not been decided whether he will be laid to rest there, or in Khilgaon.