Mohammad Reza Aref left Tehran for Doha on Friday morning to partake in the burial of Haniyeh, who was assassinated in Tehran on Wednesday.
Haniyeh was killed in a special residence in northern Tehran after being hit by an aerial projectile in the early hours of July 31.
The Hamas chief was in Tehran to attend the new Iranian president’s swearing-in ceremony.
A funeral procession was held for the Palestinian figure in Tehran on August 1. Leader of the Islamic Revolution Ayatollah Seyed Ali Khamenei led the funeral prayers for Haniyeh and his security guard.
Ayatollah Khamenei has warned the Israeli regime of a "harsh response" for Haniyeh's assassination, calling it the Islamic Republic's duty to avenge the Palestinian resistance leader's blood.