The ruling by the Arkansas Supreme Court was handed down this morning.
The court sided with 10 death row inmates who had challenged the Method of Execution (MEA) Act of 2009.
The inmates had argued that under state law, execution policy can only be set by the Legislature.
MEA gave that authority to the Department of Correction.
Death row inmate Jack Harold Jones, Jr. sued the head of the Department of Correction in 2010, challenging the law's constitutionality. Nine* other inmates then joined Jones lawsuit.
Last year, a Pulaski County Circuit Court judge struck down a portion of the law that allows the director of the Department of Correction to use any chemical in the lethal injection cocktail, saying it was unconstitutional.
Attorneys for the inmates argued certain drug combinations could make the process too painful: meaning it would be cruel or unusual punishment as defined under the U.S. Constitution.
There has not been an execution in Arkansas since 2005.
*The nine other death row inmates named in the suit are: Marcel Williams, Frank Williams, Jason McGehee, Don Davis, Bruce Ward, Stacey Johnson, Alvin Jackson, Kenneth Williams and Terrick Nooner.
Click here to read the full opinion.