Jose Medellin, 22, will die by lethal injection Aug. 5 for the 1993 murders of Jennifer Ertman, 14, and Elizabeth Pena, 16, the Houston Chronicle reported. The girls were beaten, raped and killed when they stumbled upon a gang initiation rite.
An international law expert said Medellin's execution would jeopardize U.S. foreign relations and the safety of Americans abroad.
"If we fail to keep our promises to our international partners, we lose our ability to protect our citizens abroad, and to preserve our nation's reputation as a reliable player on the world stage," Douglass Cassel, a Notre Dame presidential fellow and international law expert, said in a news release.
Medellin, born in Mexico but living mostly in Houston, had kept his appeal alive through a legal battle over international law, landing his case before the U.S. Supreme Court.
The court in March ruled President George Bush overstepped his authority when he ordered states to hear cases for 51 death-row Mexican nationals, including Medellin, claiming their rights were violated because local consulates were not notified of their arrests.