Labour MP David Shearer has been chosen to head the United Nations peacekeeping force in South Sudan.
The Mt Albert MP is therefore leaving the Government to take up the new role. It is not yet known who will stand in place in the electorate, but Jacinda Ardern is tipped to contest the seat.
Mr Shearer is giving his valedictory speech at 5:45pm on Tuesday.
United Nations Mission in South Sudan (UNMISS) is the UN's third largest peacekeeping mission with 17,000 uniformed and almost 2000 civilian personnel.
It is charged with building peace and stability in the youngest country in the world.