In 1305, Al-Hilli emigrated to Persia, to the court of the Ilkhan ruler Öljaitü, whom it is believed he converted from Sunni to Shia Islam. As a result of his conversion, Öljaitü proclaimed Shia Islam as the state religion in Persia. Coins were minted in the names of The Twelve Imams. Both al-Hilli and his son, Fakhr ul-Muhaqqiqin were engaged in extensive theological and jurisprudential debates with the local Sunni scholars. Having impressed the Ilkhan, he was appointed to the traveling "madrassah sayyarah". Al-Hilli, however, eventually returned to his hometown and spent the last years of his life teaching there.