Abadi has asked for a week to fill the missing posts, including interior and defence, during which time he will run the ministries in an acting capacity.
The previous Iraqi government also began with various posts unfilled, and acting ministers served for the next four years.
Iraq has been under heavy international pressure to approve a broad-based government to unite the various communities against a sweeping offensive led by the Islamic State (IS) jihadist group that has overrun swathes of Iraq since June.