Primus, 35, will coach Port Adelaide for the remainder of the 2010 season after Mark Williams announced he was stepping aside on Friday.
The decision on an interim coach was thought to be between Primus and former North Melbourne coach and current Port Adelaide assistant Dean Laidley.
Primus played 157 AFL games between 1996 and 2005 (20 with Fitzroy in 1996; 137 with Port Adelaide 1997-2005) and captained Port Adelaide from 2001 to 2005, although was missing from the club's premiership side in 2004 through injury.
Port Adelaide is currently in the midst of its worst losing streak in club history losing its last eight games.
Primus will front the media for the first time as Port Adelaide coach on Monday morning.