State officials had waited for a response from the Supreme Court, which had no deadline for a decision. The execution was expected to go forward about 30 minutes after the Supreme Court decision was revealed.
"We are in a delay, waiting for a decision from the U.S. Supreme Court," Peggy Chapman of the Georgia Department of Corrections told NBC News earlier. "There has not been a reprieve issued."
The state was under no obligation to wait but did so, NBC News reported.
Hundreds of Davis supporters had gathered outside the Jackson prison and lined a nearby highway. Crowds cheered and sang "We Shall Overcome" as news of the lethal-injection delay spread. Police in full riot gear were on hand to deal with any possible disturbance if the execution goes ahead.
But as the minutes, then hours, passed, the crowd dwindled to about 50.
The last-ditch effort with the U.S. Supreme Court came just 45 minutes before the execution was scheduled and after state officials refused to grant Davis a reprieve in the face of calls for clemency from former President Jimmy Carter, Pope Benedict XVI and others.
Late Wednesday afternoon, Georgia's Supreme Court had rejected a last appeal by Davis’ lawyers. Earlier, a Butts County Superior Court judge also declined to stop the execution.
Davis was convicted in the 1989 slaying of off-duty Savannah police officer Mark MacPhail.
In their U.S. Supreme Court filing, Davis' attorneys said "substantial constitutional errors" were made when the lower courts denied his claims that "newly available evidence reveals that false, misleading and materially inaccurate information was presented at his capital trial in 1989, rendering the convictions and death sentence fundamentally unreliable," NBC News reported.
The lawyers said they've been struggling to get these claims heard in the lower courts "after having a grueling clemency process."
There was no guarantee justices would act in time to stop the execution, but they likely knew the filing was coming, NBC News said.
"We're trying everything we can do, everything under the law," said Chester Dunham, a civil rights activist and talk show host protesting in Savannah, where MacPhail, 27, was killed.
Outside the Jackson prison that houses Georgia's death row, about 100 people, including the Rev. Al Sharpton, gathered Wednesday afternoon for a prayer rally. As they shouted, "Free Troy Davis!" a man in a red SUV drove by and shouted, "Kill him! Kill him!"
Several dozen people gathered outside the White House to protest the execution. They held signs condemning it as a "lynching" and chanted "Too much doubt" and "What do we want? Justice!"
Davis' execution has been stopped three times since 2007, but on Wednesday the 42-year-old appeared to be out of legal options.