Scharlette Holdman, about a week before her death. Ms. Holdman died July 12 at age 70. (Samantha Kennedy)

Scharlette Holdman, a nationally known advocate for death-row inmates who countered reports of violent crimes with the stories of the accused’s lives, revealing tragedy at the root of brutality and human beings where others saw only villains, died July 12 at her home in New Orleans. She was 70.

The cause was gallbladder cancer, her children said.

In the community of activists who serve U.S. prisoners facing execution, Ms. Holdman was among the most dogged, most enterprising and most influential, despite her lack of formal legal training.

Over more than four decades — “fueled by cigarettes, caffeine, alcohol and nerves,” in the description of journalist and author David Von Drehle — she used her background in anthropology to pioneer the legal strategies now employed across the United States in the defense of death-row inmates.

Ms. Holdman traced her social conscience to her childhood in Tennessee. She recalled that her father, a white landlord, took pleasure in evicting black tenants. She came to oppose the death penalty not primarily on moral grounds, but rather because of the inequities she saw in the way it is handed down.

“How willing is a country that wants the death penalty to ignore the risk of a wrongful conviction?” she once told the Toronto Star. “No system can eliminate the human error and human prejudice that can lead to the irreversible destruction of human life.”

Ms. Holdman rose to prominence in the 1970s as head of the Florida Clearinghouse on Criminal Justice, a Tallahassee operation with an annual budget of less than $25,000 and a largely volunteer workforce. Legal briefs were sometimes printed on paper that Ms. Holdman had scavenged from library wastebaskets.

At the time, the death penalty in the United States was undergoing a historic shift. After suspending capital punishment in 1972, the U.S. Supreme Court reinstated it in 1976, with the proviso that courts must consider the aggravating and mitigating circumstances of a defendant’s case before he or she could be sentenced to death.

Dubbed by others the “Mistress of Delay” and “the Angel of Death Row,” Ms. Holdman called herself and others in her role a “mitigation specialist.”

She would work with a defendant’s lawyer or, more often, work the phones to track down a lawyer when a defendant did not have one. For Christmas, a colleague once gave her a phone receiver cushion, worrying that she might develop cauliflower ear, Von Drehle wrote in his book “Among the Lowest of the Dead: The Culture of Capital Punishment” (1995).

As the lawyer navigated the legal intricacies of a death-row defense, Ms. Holdman would prepare a multigenerational family history, unraveling the forces that might have led a defendant to commit a violent crime. In many cases, she found that offenders were also victims.

“Not all of them are nice people. But some are among the finest human beings I’ve ever met, in prison or out of prison,” she told the Miami Herald. “Some have become good friends. See, all of us evolve. People on Death Row grow older, they grow wiser.”

Robert Dunham, executive director of the Washington-based Death Penalty Information Center, credited Ms. Holdman with creating a model for the life-history investigations that the American Bar Association now considers standard in death penalty defense work.

“Juries want to kill monsters. They have a very hard time giving the go-ahead to kill somebody they see as a vulnerable human being,” Dunham said in an interview.

Ms. Holdman stayed out of the spotlight, in the courtroom and elsewhere.

The most high-profile defendants she served included Theodore J. Kaczynski, known as the Unabomber, who expressed a wish to gift her his Montana cabin; Eric Rudolph, who confessed to perpetrating bombings at the 1996 Atlanta Olympics and at abortion clinics; Jared L. Loughner, who pleaded guilty in the 2011 shooting that wounded then-Rep. Gabrielle Giffords (D-Ariz.); and Dzhokhar Tsarnaev, who was convicted in the 2013 Boston Marathon bombing.

She also contributed to the defense of Khalid Sheikh Mohammed, the accused mastermind of the terrorist attacks of Sept. 11, 2001. She converted to Islam in solidarity with people “who have been unjustly scrutinized and persecuted by the government,” her daughter, Summer Lindzey, said, and received a Muslim burial.

Scharlette Jane Holdman was born in Memphis on Dec. 11, 1946. Her father ran laundries and a plumbing operation in addition to renting properties.

“I come from a family whose religion is racism. I don’t mind you saying that; we’re quite estranged,” Ms. Holdman told the Herald. “They detest the work I’m doing. . . . They built their entire fortune on the backs of black people.”

In high school, Ms. Holdman was yearbook editor and cheerleading captain. She later reacted against her upbringing by participating in voter registration drives in the South and antiwar marches in Washington and by working for the American Civil Liberties Union.

She described feeling stifled by marriage and was divorced from her only husband, James Shotwell Lindzey Jr. Survivors include their two children, Summer Lindzey of New Orleans and James “Tad” Lindzey III of Medellin, Colombia; two sisters; and a granddaughter.

After her work in Florida, Ms. Holdman led death penalty defense efforts in San Francisco and New Orleans.

At times, her detractors saw her as having befriended evil, even as having subverted justice in her efforts to pursue it. Even Ms. Holdman said that she occasionally asked herself if she had “gone too far.”

“I reanalyze it all the time,” she told Newsweek magazine in 1981. “I’m glad I always end up thinking what I’m doing is right.”