Abadi declared Nineveh liberated in its entirety after Iraqi security forces captured hills of a Tal Afar sub-district.
"Our brave Armed Forces have liberated Tal Afar and the Iraqi flag is once again flying high in Nineveh province," Abadi said in a statement. "I salute our martyrs, our injured and their families whose sacrifices have made this and other victories possible. Nineveh is liberated."
Abadi thanked Iraq's security forces involved in the operations -- the Iraqi Army, Federal Police, Counter-Terrorism and Rapid Response forces -- and the Hashd al-Shaabi Shiite-led militia for helping liberate the segments of the province captured by the Islamic State in June 2014.
Iraqi forces on Sunday declared victory in the northern city of Tal Afar eight days after the offensive to capture the city began.
Iraq launched its military offensive to retake Mosul -- Iraq's second-largest city -- from the Islamic State, also known as Daesh, ISIL and ISIS, on Oct. 17.
The offensive was led by Iraqi security forces and aided by the Kurdish Peshmerga, the Shiite-led militia, and the U.S.-led international coalition. Iraq declared victory in Mosul in July.