Texas defied the World Court and executed a Mexican national by lethal injection on Tuesday over the objections of the international judicial body and neighbouring Mexico.
José Medellin, 33, was pronounced dead at 9.57 p.m. CDT (0257 GMT) in the state's death chamber in Huntsville, the Texas Department of Criminal Justice said.
He had been condemned for the 1993 rape and murder of 16-year-old Elizabeth Pena in Houston and lost his bid late Tuesday for a last-minute stay from the US Supreme Court.
The World Court last month ordered the US government to "take all measures necessary" to halt the upcoming executions of five Mexicans including Medellin's on the grounds that they had been deprived of their right to consular services after their arrests.
Mr Medellin's execution is sure to anger neighbouring Mexico and analysts have said it could make life rough for Americans arrested abroad if other countries decide to evoke the US example and deprive them of their right to consular services.
This typically means diplomats will visit and provide legal advice to their nationals being held by authorities.
The Texas Board of Pardons and Paroles had recommended that the state's Republican governor Rick Perry not grant a temporary reprieve, paving the way for Mr Medellin's execution.
Texas, which executes far more convicts than any other US state, had taken the view that the brutal nature of Medellin's crimes rendered him unfit for a reprieve or lesser sentence.
The World Court's jurisdiction also does not reach Texas, a state where authorities generally don't like outsiders telling them what to do.
The political fall-out from the Medellin and related cases has reached the White House and the US Supreme Court.
US President George W. Bush directed his native Texas to comply with a World Court ruling in 2004 mandating review of the cases of Mr Medellin and other Mexicans in US prisons awaiting execution. The US Supreme Court said in March Bush's action had exceeded his authority.
The government of Mexico sent the US State Department a diplomatic note of protest, expressing "its concern for the precedent" that the case "may create for the rights of Mexican nationals who may be detained in that country."
The June 1993 crime for which Mr Medellin was condemned was chilling. According to the Texas Attorney General's office, Pena and her 14-year-old companion, Jennifer Ertman, were walking home when they encountered a gang initiation.
Mr Medellin and his fellow gang members sexually assaulted, beat and strangled the two girls. When their badly decomposed bodies were finally recovered, they could only be identified by dental records. Mr Medellin was only convicted of Pena's murder.