Abu Jaafar al-Maqdesi was killed earlier this month, the group’s Aamaq news agency announced late on Sunday, without disclosing where or under what circumstances.
A photo of a young bearded man accompanied the report.
Egypt has been battling militants for years but the Sinai-based insurgency gained strength after the 2013 overthrow of the country’s first elected Islamist president, Mohammed Morsi.
In February, Egypt launched a massive operation against militants in Sinai as well as parts of the Nile Delta region and the Western Desert, along the porous border with Libya.
Earlier this month, Egypt’s military court heard the trial of 292 detainees accused of forming 22 armed cells belonging to the Islamic State group’s Sinai branch who allegedly planned to assassinate Sisi.
Prosecutors claimed the detainees, including six police officers, established an armed group operating under the banner of IS in the Sinai region, which planned to assassinate Sisi on two occasions.
One of the plans involved a scheme to kill Sisi during his umrah pilgrimage alongside Saudi Prince Mohammed bin Nayef in Saudi Arabia’s holy Mecca city, while the second included a cell of six on-duty police officers who would target the Egyptian leader while passing through a Cairo street.
The cell allegedly pledged allegiance to IS leader Abu Bakr al-Baghdadi before becoming an affiliate of the militant group.
More than 200 suspected jihadists and at least 35 soldiers have been killed since Egypt launched operation “Sinai 2018” to rid the peninsula of Islamic militants in February, according to the military.