JACKSON, Ga.—Troy Anthony Davis, convicted of killing a Savannah police officer more than two decades ago, was executed by lethal injection Wednesday evening, less than an hour after the U.S. Supreme Court declined to intervene.

People in Jackson, Ga. reacted to the news of Mr. Davis's execution. Associated Press

Mr. Davis was pronounced dead at 11:08 p.m. local time, and his death brought to a conclusion a case that became a cause for anti-death penalty advocates around the world.

The execution began at 10:53 p.m., according to pool reporters who were present. Also on hand were two family members of the officer slain in 1989 by Mr. Davis—Mark Allen MacPhail—and they stared at him throughout the process.

"I am innocent," Mr. Davis told them.

His last words were to the prison staff administering the injection: "May God have mercy on your souls. May God bless your souls."

The scheduled 7 p.m. execution of Mr. Davis was delayed after attorneys for Mr. Davis sought a last-minute request with the Supreme Court.

As word of the court's ruling reached the often tense scene outside the prison where the execution had been scheduled, hundreds of corrections officers and state troopers in riot gear stood at attention. Facing them from across the street were about a thousand protesters.

In their appeal, lawyers for Mr. Davis said they planned to file a brief that allegedly would disclose new evidence establishing that "false, misleading and materially inaccurate information" was presented at Mr. Davis's murder trial in 1991.

By 6:30 p.m. Wednesday, a throng of Davis supporters, including the Rev. Al Sharpton, gathered in a roped-off area at the entrance of the Georgia Diagnostic and Classification Prison near Jackson. They gave speeches and prayed for Mr. Davis.

Earlier, Mr. Sharpton said he was interested in the Davis case because of "the wrongness of it. This isn't an issue of black or white." Mr. Davis, 42 years old, was black. Mr. MacPhail, the 27-year-old man he was convicted of shooting to death, was white.

Stationed in another area near the entrance were a handful of those in favor of Mr. Davis's execution. Among them was Janet Reisenwitz, 55, of Decatur, Ga., who said she drove to the prison in support of the MacPhail family.

"As a mother of a police officer, I know I'm doing the right thing," she said.

The families of victims are often forgotten in such cases, she said, and "my heart goes out to the MacPhail family."

The case had attracted world-wide interest from death-penalty opponents—including Pope Benedict XVI and former President Jimmy Carter. Many questioned the strength of the prosecution's case in light of recantations by witnesses.

Mr. Davis was sentenced to death in 1991 for the murder of Mr. MacPhail, an Army veteran and father of two small children. Mr. MacPhail was shot in a Burger King parking lot in Savannah.

After the killing, multiple witnesses testified that Mr. Davis committed the murder.

Years later, several witnesses recanted or altered their testimony.

Mr. Davis has faced execution three times before, and was spared each time by appeal efforts.

In 2009, the U.S. Supreme Court ordered a lower federal court to review the case and to let Mr. Davis prove his innocence.

A federal judge in Savannah in 2010 reviewed the recantations and other material and ruled them "largely smoke and mirrors."

—Nathan Koppel and Jess Bravin contributed to this article.

Corrections & Amplifications
Troy Davis's murder trial occurred in 1991. An earlier version of this article incorrectly said the trial took place in 1989.