U.S. District Judge Lee Rosenthal in Houston agreed to delay the scheduled punishment for 90 days after the Texas Court of Criminal Appeals had rejected the appeal Monday.
Rosenthal said Eldridge's lawyers made a "substantial threshold showing of insanity" and should be given a hearing. The Supreme Court has ruled in previous cases that mentally ill prisoners may be executed if they are aware of why they are facing the punishment.
"Eldridge is entitled to an opportunity to submit evidence and arguments, including expert psychiatric evidence, on the question of insanity," Rosenthal wrote in a 10-page ruling.
Eldridge received word of the reprieve while he was in a small cell just outside the death chamber in Huntsville. He immediately was taken back to death row at the Texas Department of Criminal Justice Polunsky Unit, about 45 miles to the east.
"He was making a phone call and had eaten most of his last meal," Texas prisons spokesman Jason Clark said. "He was emotional. He got a little choked up when the news was relayed to him."
Eldridge was convicted of capital murder for a January 1993 shooting spree that killed his former girlfriend, 28-year-old Cynthia Bogany, and her 6-year-old daughter, Chirissa. Also wounded in the gunfire was Terrell Bogany, Eldridge's then-7-year-old son with Bogany, and the woman's boyfriend at the time, Wayne Dotson.
Eldridge would have been the 22nd prisoner executed this year in Texas and the first of three scheduled to die this week.
"He's completely detached from reality," lawyer Lee Wilson said.
He "has consistently and historically feigned mental illness in order to avoid the consequences of his criminal behavior," Inger Hampton, an assistant Harris County district attorney, said in court filings.
Terrell Bogany testified at Eldrige's trial, describing how his father kicked in the door of their apartment, that he tried to cover himself and was shot in the shoulder, and his half-sister, asleep on a couch, was shot between the eyes.
Terrell Bogany also described Dotson being shot and seeing his mother run from the apartment with Eldridge in pursuit. Evidence showed Cynthia Bogany was shot outside as she tried to flee to a neighboring apartment.
A psychologist who recently examined Eldridge for his lawyers concluded Eldridge may have a significant psychotic disorder. Prosecutors, however, pointed out the psychologist also said it wasn't possible to reach an opinion regarding his competence for execution.
Records showed Eldridge was sentenced in 1985 to eight years in prison for an earlier shooting spree in which three men were wounded, including one who was shot eight times. He was released three years later, then returned to prison in 1990 for beating his son. He was paroled after four months.
On Wednesday, Danielle Simpson, 30, is scheduled for execution for the January 2000 abduction and slaying of an 84-year-old East Texas woman.
A day later, Robert Lee Thompson, 34, is scheduled to die for his part in the shooting death of a Houston convenience store clerk during a robbery 13 years ago.