A Cairo appeal court has upheld a lower court's decision to dismiss prosecutor-general Talaat Abdullah.
The court also rejected former prosecutor-general Abdel-Meguid Mahmoud's appeal to be reinstated to the post.
Assistant prosecutor-general Hassan Yassin will hold the top position until Egypt's Supreme Judicial Council (SJC) convenes to make an official appointment.
In March, a court reversed President Mohamed Morsi's November 2012 decision to appoint Abdullah in Mahmoud's place via a controversial constitutional declaration.
Judicial critics said only the SJC has the power to appoint the prosecutor-general and therefore President Morsi had acted beyond his mandate when appointing Abdullah to the post.