Abu-Jamal was sentenced to death nearly 30 years ago for killing Philadelphia police officer Daniel Faulkner.
The inmate's case has been up and down the appeals court ladder many times, but last May the 3rd U.S. Circuit Court of Appeals ruled Mumia Abu-Jamal's death sentence was unconstitutional because his jury was given confusing instructions.
Philadelphia District Attorney Seth Williams said he would ask the U.S. Supreme Court to review the appeals court ruling, but that request was denied Tuesday.
"This decision marks an important step forward in the struggle to correct the mistakes of an unfortunate chapter in Pennsylvania history," said John Payton, director-counsel of the NAACP Legal Defense Fund, which is representing Abu-Jamal.
In a statement, the NAACP Legal Defense & Educational Fund said the high court's rejection "brings to an end nearly 30 years of litigation over the fairness of the sentencing hearing that resulted in Mr. Abu-Jamal's being condemned to death. Mr. Abu-Jamal will be automatically sentenced to life in prison without the possibility of parole unless the district attorney elects to seek another death sentence from a new jury."
Abu-Jamal's case now returns to the Philadelphia County Court of Common Pleas for final sentencing.