The U.S. Supreme Court decided not to spare a Texas man from a lethal injection on Tuesday.
Adam Ward's attorneys said he's delusional and should not be put to death because of his mental illness.
They said their client was defending himself when he killed a city code enforcement officer in June 2005.
His lawyers argued that a ban on executing mentally impaired prisoners should be extended to him, but the Supreme Court has denied that appeal.
The 33-year-old is scheduled to be put to death within the hour, it would be the fifth execution this year in Texas and the ninth nationally.