McCarthy, 51, was to be executed Tuesday by lethal injection at the Texas State Penitentiary in Huntsville for the July 21, 1997, slaying of her neighbor, retired college Professor Dorothy Booth, 71.
Dallas County Judge Larry Mitchell rescheduled the execution for April 3 after University of Texas law Professor Maurie Levin argued McCarthy, who is black, was a victim of racial discrimination when a jury of 11 whites and one black convicted her, KWTX-TV, Waco, reported.
Prosecutors -- who had argued the record does not support the defense argument of discrimination -- said they will not appeal the ruling, KWTX-TV said.
McCarthy was convicted of beating Booth to death with a candelabra then cutting off the victim's finger to steal her wedding ring.
After McCarthy was arrested for Booth's slaying, Dallas police linked her to two other fatal stabbing-robbery cases from 1988, WFAA-TV, Dallas, said.
McCarthy was convicted of Booth's murder in 1998. Her conviction was overturned in 2001, but she was found guilty a second time a year later and sentenced to die for Booth's murder. The conviction and sentence stood as the case moved through the appeals process.
McCarthy is one of 10 women on death row in Texas, the Death Penalty Information Center said. Twelve women have been executed in the United States -- four of them in Texas -- since the U.S. Supreme Court reinstated the death penalty in 1976, the center said on its website.