Dylann Roof has been sentenced to death for killing nine black church members in Charleston, S.C.
He is the first person to get the death penalty for federal hate crimes.
The jury reached a decision after about three hours of deliberations.
Earlier Tuesday, Roof threw away a chance to plead for his life, telling jurors: "I still feel like I had to do it."
Roof walked to the podium less than three metres from the jury box with a yellow sheet of paper. He put it down and looked past jurors for about 30 seconds before beginning to read off the page.
Every juror looked directly at Roof as he spoke for about five minutes. A few nodded as he reminded them that they said during jury selection they could fairly weigh the factors of his case. Only one of them, he noted, had to disagree to spare his life.
"I have the right to ask you to give me a life sentence, but I'm not sure what good it would do anyway," he said.
Roof paused several times, but jurors never took their eyes off him. After one of the pauses, he abruptly said, "That's all," quickly gathered his sheet of paper and walked back to the defence table.
After more than two hours of discussions they re-watched a speech by one of the victims, Clementa Pinckney, the church pastor and a state senator. In it, Pinckney talks about the history of Emanuel and its mission.
Jurors also asked if Roof could safely be confined if he were sentenced to life in prison. The judge told them to re-read the instructions he provided them to figure out what the mitigating factor means.
The attacker specifically picked out Emanuel AME Church, the South's oldest black church, to carry out the cold, calculated slaughter, assistant U.S. attorney Jay Richardson said.
The 12 people Roof targeted on June 17, 2015, opened the door for a stranger with a smile, he said. Three people survived the attack.
"They welcomed a 13th person that night ... with a kind word, a Bible, a handout and a chair," Richardson said during his closing argument. "He had come with a hateful heart and a Glock .45."
The gunman sat with the Bible study group for about 45 minutes. During the final prayer — when everyone's eyes were closed — he started firing. He stood over some of the fallen victims, shooting them again as they lay on the floor, Richardson said.
The prosecutor reminded jurors about each one of the victims and the bloody scene that Roof left in the church's lower level.
The jury convicted him last month of all 33 federal charges he faced, including hate crimes. Roof, 22, would be the first person to get the death penalty for federal hate crime convictions.
Roof did not explain his actions to jurors, saying only that "anyone who hates anything in their mind has a good reason for it." In his FBI confession, Roof said he hoped the massacre would bring back segregation or start a race war.
Nearly two dozen friends and relatives of the victims testified during the sentencing phase of the trial. They shared cherished memories and talked about a future without a mother, father, sister or brother. They shed tears, and their voices shook, but none of them said whether Roof should face the death penalty.
Richardson recalled Jennifer Pinckney's remarks about her husband, Clementa, who was remembered for singing goofy songs and watching cartoons with their young daughters in his spare time. He was the church pastor and a state senator.
Roof acted as his own attorney and did not question any witnesses or put up any evidence.
The last person sent to federal death row was Boston Marathon bomber Dzhokhar Tsarnaev in 2015.