The execution of Russell Bucklew, 46, had been scheduled for just after MIDNIGHT.
U.S. Supreme Court Justice Samuel Alito granted a stay of execution for the convicted killer.
Bucklew's lawyers argued that a birth defect, cavernous hemangioma, could have caused a "prolonged and excruciating execution."
The stay of execution came after Missouri Governor Jay Nixon had denied a petition for clemency for what he called the heinous nature Bucklew's crimes.
In 1997, Bucklew was convicted of raping his ex-girlfriend, killing a man he believed to be her new boyfriend and shooting a gun at that man's six year old son.
Bucklew's killing spree ended with a shootout with the Missouri State Highway Patrol that left a trooper wounded.
On Monday, another judge had denied a request to stay the execution and a request to have the execution videotaped.
Bucklew's execution would have been the first since a botched lethal injection in Oklahoma last month and Missouri's seventh execution since last November.
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