Mack Arthur King, now 53, was sentenced to die by a Lowndes County jury in the death of 84-year-old Lela Patterson in 1980. Patterson was beaten, strangled and drowned at her home during a burglary.
King had his conviction and sentence overturned on two previous appeals.
He was tried and convicted for a third time in 2003 and sentenced to death.
King has claimed he suffers from mental issues and is barred from receiving the death penalty.
A federal court judge on Friday ordered King to be evaluated by a doctor with the state of Mississippi.
He has already been evaluated by a doctor as part of his defense.