Earlier his son, Ammar, said that he was in 'critical health condition' due to lung cancer.
The death of Hakim will add to political uncertainty ahead of national polls in January and after a series of devastating bombings.
Hakim was hospitalized in an advanced medical faculty in Tehran last month.
Mohsen Hakim told IRNA that his brother, Ammar Hakim, arrived in Tehran and attended at his father's bedside.
The Shia political figure, who heads Iraq's most powerful party, was diagnosed with lung cancer in a Texas hospital in the United States.
Following the diagnosis, he made several trips to Iran for chemotherapy before being hospitalized.