Hassan Rouhani has declared Islamic State is dead in a live statement on television.
The Iranian President made the declaration on state media, while a general in the army, Qassem Soleimani, also said Isis had been defeated.
It is unclear which announcement was made first or when the information was given to the two.
In the president's statement, he thanked the "warriors of Islam" for their assistance in ending the group.
Isil has been subjected to two ongoing military campaigns over the last few years and has been steadily losing ground gained under a rapid advance in 2014.
On Sunday, Reuters reported Syrian forces and allied military groups took control of Albu Kamal, the last significant town under the terror group's control in Syria.
Despite this declaration from the president of Iran and its military, western intelligence has warned the group may still be able to inspire attacks on citizens across the globe.