The shooting took place the Burnette Chapel Church of Christ in Antioch, a neighborhood in Davidson County governed by Nashville.
A gunman in the church parking lot shot and killed Melanie Smith, 39, as she was walking to her car when a prayer service was letting out.
The shooter then entered the church through the sanctuary's main door with two pistols and "began indiscriminately shooting," Metropolitan Nashville Police Department spokesman Don Aaron said.
There were approximately 50 people still inside the sanctuary when the shooting began. Six were wounded by gunfire and another was pistol-whipped, Aaron said.
Church usher Robert Engle, 22, saw the shooting and confronted the gunman, Aaron said. During a struggle, the gunman mistakenly shot himself.
"It would appear he was not expecting a brave individual like the church usher to initiate the struggle and confrontation," Aaron said.
Motive not yet established
Suspect Emanuel Kidega Samson, 25, was hospitalized for gunshot wounds and released to police custody.
He was charged with felony homicide and was being held without bond, police said. Other charges are coming later, according to police. His next court appearance is Wednesday.
The Department of Justice and the FBI have opened a federal civil rights investigation of the shooting and police said they were still trying to establish the gunman's motive.
Local police also requested the assistance of the Bureau of Alcohol, Tobacco, Firearms and Explosives to run an "urgent trace" on a firearm, an ATF spokesperson told CNN.
The trace would give authorities an indication of where the gun was purchased, who purchased it and whether it was purchased legally, the spokesperson said.
Police initially said the suspect was African-American. Later, police identified him as Sudanese with legal US residency.
Church members told police that Samson attended the church one to two years ago, Aaron said. But they had not seen him in a while and did not immediately identify him as the shooter because the gunman was masked.
Usher 'a hero'
Minerva Rosa, who was inside the church when the shooting started, told reporters Sunday the gunman was silent when he opened fire.
Without Engle, the usher who tackled the gunman, "I think it could be worse," she said. "He was a hero today."
MNPD chief Steve Anderson echoed the sentiment at a press conference.
"He's the hero," Anderson said. "He's the person that stopped this madness, so we're very, very, very grateful to him."
Engle released a statement through the hospital where he was treated.
"I've been going to this church my whole life, since I was a small child," he said. "I would have never, ever thought something like this would have happened."
He asked for prayers for the victims and their families, adding, "please pray for the shooter, the shooter's family and friends. They are hurting as well."
Engle said he did not want to be labeled a hero. "The real heroes are the police, first responders and medical staff and doctors who have helped me and everyone affected."
Nashville mayor Megan Barry said in a tweet that the shooting was "a terrible tragedy for our city."
"My heart aches for the family and friends of the deceased as well as for the wounded victims and their loved ones," she said. "Their lives have been forever changed, as has the life of their faith community at Burnette Chapel Church of Christ."
Vigil planned Monday
The first call reporting multiple gunshots came in around 11:15 a.m. CT, police said.
Joe Love, a man who lives near the church but did not see the shooting, told CNN affiliate WKRN that he became aware of it when a frantic man and his wife who had both been inside the church came to his door on Sunday.
"The guy shot at them," but they were able to flee, said Love, who is not a parishioner. The two weren't hit.
Love said he raced over to the church, and the gunman had already shot himself. He said he recognized the slain woman; she was a familiar face at the church.
Love said he helped the victim's sister cover up the deceased woman with towels "so she wouldn't be disgraced anymore."
A church member who walked CNN through the parking lot overnight pointed to a green SUV that Smith fell against after she was shot, breaking its mirror.
Another SUV in the carpark belonged to two shooting survivors, the parishioner said. A Bible on the ground had been Smith's.
There will be a vigil for victims at the church Monday at 7 p.m. local (8 p.m. ET).
This story has been updated to include more details from the police regarding the suspect's background.