Ismail Alwan Salman al-Ithawi, 55, was tracked to Turkey's Sakarya region, detained and returned through cooperation between Turkish, Iraqi and US intelligence agencies, a senior official in the interior ministry's Falcons unit hunting IS members told AFP.
The break came after his unit had "infiltrated the highest levels" of the jihadist group, he said.
A native of the Iraqi city of Ramadi, Ithawi was the group's "minister" in charge of religious edicts and headed a IS committee that decided on senior appointments, according to the official. He had fled the group's now-shattered "caliphate" in Syria and was living under his brother's name in northern Turkey.
"We asked our ambassador in Ankara to intervene with the Turkish authorities by providing the arrest warrant issued by Iraqi courts and recent photos of Ismail," the official said.