Turkey's president says the first prayers will be held inside the building on July 24, after he signed a decree formally restoring the landmark's status as a mosque.
On Friday, a court ruled its conversion to a museum in 1934 was illegal.
It was the biggest Christian cathedral in the world for nearly 1,000 years and is considered the pinnacle of Byzantine architecture.
Last year, the museum was Turkey's most visited tourist site.
Al Jazeera’s Sinem Koseoglu reports.

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