BOSTON — Lillian Bonner Sutson, a little-known civil rights activist whose attempts to register as a voter in South Carolina set a precedent in the fight against segregation and voting discrimination in the South, has died in Massachusetts, her family announced Wednesday.

Sutson died of age-related causes Monday at a nursing home in Saugus. She was believed to be 99, said her grandson, Marcus Jones.

In 1940, Sutson, the granddaughter of a slave, went with her mother and two other African-American women to register as Democrats in Gaffney, S.C. They were denied, threatened and verbally abused, sparking a federal criminal case. Thurgood Marshall served as their attorney in the case during which the women endured death threats that sometimes warranted FBI protection.

They lost, but Marshall eventually used the experience in civil rights lawsuits that ultimately helped strike down voter discrimination and segregation.

Her efforts were cited in a letter from First Lady Michelle Obama shortly before the president's second inaugural, Jones said.

"Your example of service shows ... that each of us can make a difference for those around us," Obama wrote, according to Jones.

Two years earlier, Massachusetts Gov. Deval Patrick, the state's first black elected governor, paid tribute to Sutson, who lived there the last 50 years of her life.

"Your act of courage was uniquely American and uniquely human, a voice of reason rising above the din of ignorance and intolerance," Patrick said. "Like so many others who are humbled by your acts of heroism, I am grateful for your sacrifices. Your bravery made countless opportunities come alive for future generations."

Sutson's feisty spirit was highlighted in 2011 when she fought off an assailant who attacked and robbed her at her home in Lynn. Sutson managed to stab the intruder in the thigh during the struggle and screamed for help as he fled.

She suffered head lacerations that required 14 stitches to close. A suspect was eventually arrested in the case.

Sutson was alert and competent up to the last days, Jones said.

"We just wanted others to appreciate the legacy that she left behind," he said.

A wake was scheduled for Friday in Lynn, and a service was planned for Tuesday in Gaffney. Sutson's remains will be sent there for burial.