In a message on Tuesday, the Supreme Leader hailed Ayatollah Mahdavi Kani as a "pious cleric, sincere politician and outspoken revolutionary" who spared no efforts to defend the causes of the Islamic Revolution.
Earlier in the day, Iranian President Hassan Rouhani declared two days of national mourning in commemoration of Ayatollah Mahdavi Kani.
Ayatollah Mahdavi Kani had been admitted to the hospital on June 4 after suffering a heart failure and went into a coma afterwards. He died of cardiac arrest at the age of 83.
Back in 2011, Ayatollah Mahdavi Kani was elected as the chairman of the Assembly of Experts, a high-ranking body of experts which elects and oversees the activities of the leader of the Islamic Revolution.
The leading cleric was a close ally of the founder of the Islamic Republic, the late Imam Khomeini, and played a major role in events that culminated in the 1979 Islamic Revolution.