Gloria Richardson, a firebrand civil rights activist who drew national attention in the early 1960s in a showdown on Maryland’s Eastern Shore that presaged the Black Power movement and led to a year-long imposition of martial law, died July 15 at her home in Manhattan. She was 99.

Her daughter Tamara Richardson confirmed the death but did not give a cause.

Ms. Richardson spent the past five decades in relative obscurity, having admittedly burned out after her front-line leadership role in Cambridge, Md. She left in 1964 and spent much of her life working on anti-poverty issues and programs for the aging in New York City.

But for the three years in which Ms. Richardson galvanized protests against racial segregation and fought for economic justice for Cambridge’s 4,200 Black residents, she not only was a spearhead for civil rights in her community, but she also helped set off a national furor over the direction of the civil rights struggle.

In particular, the uprising in Cambridge straddled a fault line between advocates for nonviolence, such as the Rev. Martin Luther King Jr., and more extreme leaders such as Malcolm X, whom Ms. Richardson considered a friend and supporter. Calling herself “a radical, a revolutionary,” she also was reportedly one of the few women leading a local civil rights protest movement at the time. Her embrace of all tactics — negotiations and force — did not go over well with mainstream civil rights groups and liberal-minded religious figures, who sometimes likened the militant approach to vigilantism.

President Lyndon B. Johnson and Senate leaders shepherding a comprehensive civil rights bill condemned militancy as counterproductive to the cause of justice, saying in a joint statement, “Civil wrongs do not bring civil rights.”

Ms. Richardson, then a 39-year-old divorced mother of two in Cambridge, emerged as an activist by happenstance. She came from a prosperous family ingrained in the community’s business life and political affairs. A grandfather had served decades on the town council representing an all-Black ward of Cambridge.

She was working in her father’s drugstore when the Student Nonviolent Coordinating Committee, a nationwide civil rights group known as SNCC, and the Freedom Riders, who rode interstate buses to confront segregation, targeted Cambridge in 1961.

When another relative left the role, Ms. Richardson assumed the chairmanship of a SNCC affiliate, the Cambridge Nonviolent Action Committee — a misnomer, given the organization’s belief in violence as an agent of change. Although she professed an initial fear of public speaking, she emerged as one of the country’s most unyielding voices for civil rights.

In the 1960’s, Gloria Richardson emerged as one of the nation’s leading civil rights fighters. Now, at 98, she talks about how she sees U.S. race relations. (Amber Ferguson/The Washington Post)

Ebony magazine dubbed her “the lady general of civil rights.” And she was, indeed, defined by a steely independent streak that did not kowtow to outsiders, whether established civil rights figures or the leader of the free world. Her only constituency, she said, was African Americans facing severe poverty and racism in Cambridge.

Ms. Richardson not only pressured city, county, state and federal officials on racial desegregation, but she also heavily emphasized “bread and butter” issues such as housing, jobs and health care.

The town’s largest employer, a packing plant, had closed, and Black unemployment had reached about 30 percent in 1961. The community’s sole Black police officer wasn’t allowed to arrest Whites, and many poor Blacks lived in converted chicken coops with no running water in Dorchester County, of which Cambridge (population 13,000) remains the county seat.

By the summer of 1963, simmering racial tensions began to erupt into violent clashes — involving shootings, arsons and the throwing of molotov cocktails — between Blacks and Whites. Ms. Richardson clamored for President John F. Kennedy to visit the town “to avert civil war.”

When she was summoned to the White House, she later recalled warning the attorney general, Robert F. Kennedy, that it would be fruitless to make deals with King or other major civil rights leaders.

“These national leaders cannot make any agreement with you,” she told Kennedy, according to a published account about female civil rights activists, “Hands on the Freedom Plow.” “They can participate, but they can’t have the final say. It’s us. It doesn’t matter what anybody else says. It’s our bodies out in the streets.”

When a King emissary arrived, she sent him packing. She was subsequently sidelined at the August 1963 March on Washington, where King gave his “I have a dream” speech. “When I was called to speak,” she recalled, “I went to the front, picked up the microphone, and all I was able to say was ‘Hello.’ Before I could say another word, an NAACP official took the mic away.”

(In another interview, she likened the march to a “big party” and a “picnic” in contrast to what she endured in Cambridge.)

The Maryland governor, J. Millard Tawes, declared martial law in June 1963, bringing in hundreds of National Guard troops, some of whom would be wounded in the strife. Ms. Richardson once shoved a bayonet-tipped rifle away from her face as she tried to calm a crowd of Black protesters — an image, captured by a news photographer, that symbolized her fearlessness.

While the soldiers tried to enforce calm, Robert Kennedy and his top aides helped broker an accord calling for the racial desegregation of schools, housing and employment. It was called the “Treaty of Cambridge.”

But Ms. Richardson remained uncompromising in her demands for equal access to public accommodations such as White-owned restaurants and bowling alleys. A public-accommodations provision went to referendum in October 1963, but she persuaded followers to boycott the vote. She explained that it was grossly unfair to leave “the constitutional rights of our people to the whim of a popular majority.”

The provision was overwhelmingly defeated, with 70 percent White turnout and low Black turnout. Some critics blamed her for the loss, and the issue was left unresolved, stoking further resentment on all sides.

“The status quo is now intolerable for Negroes and may soon be intolerable for the majority of whites,” she ominously warned to Ebony.

Cambridge was further destabilized by a May 1964 visit from George C. Wallace, the segregationist Alabama governor then seeking the Democratic presidential nomination. Ms. Richardson was among those tear-gassed and arrested by the National Guard for street protests that turned unruly.

By summer, the first campaign for the “Battle for Cambridge,” as it was widely called, was coming to a denouement. The Civil Rights Act of 1964 was signed by Johnson that July, and the National Guard troops began their withdrawal.

That year, Ms. Richardson relinquished her role with the Cambridge Nonviolent Action Committee after marrying a freelance photographer, Frank Dandridge, who covered the protests. She left the spotlight but maintained her aggressive approach to civil rights activism for decades, calling on a younger generation of protesters to do more after the killing of George Floyd in 2020.

“Racism is ingrained in this country. This goes on and on,” she told The Washington Post last year. “We marched until the governor called martial law. That’s when you get their attention. Otherwise, you’re going to keep protesting the same things another 100 years from now.”

Gloria St. Clair Hayes was born in Baltimore on May 6, 1922, and grew up in Cambridge, where her pharmacist father relocated during the Depression. The area had a storied history for African Americans. The abolitionist Harriet Tubman was born into slavery in Dorchester County, and the area was a stop on the Underground Railroad.

As a child, Gloria showed early signs of dissent. After a spate of lynchings on the Eastern Shore, she refused to stand for the Pledge of Allegiance because she believed that its promise of “liberty and justice for all” did not apply to Blacks.

She studied sociology at Howard University and, after her graduation in 1942, became a federal civil servant. While in Washington, she and others picketed a segregated Woolworth’s store. She returned to Cambridge but found herself blocked from employment there with the Maryland Department of Social Services.

She married a schoolteacher, Harry Richardson, in 1948, and they had two children before divorcing. Her marriage to Dandridge also ended in divorce. In addition to her daughter Tamara Richardson, of Manhattan, survivors include another daughter, Donna R. Orange of Columbia, Md.; two granddaughters; and a great-grandson.

Joseph R. Fitzgerald, an assistant professor of history and political science at Cabrini University in Pennsylvania and the author of the 2018 book “The Struggle Is Eternal: Gloria Richardson and Black Liberation,” called Ms. Richardson “a trailblazer” whose protests “laid groundwork for later militant struggles and the Black Power movement.”

In 1967, Ms. Richardson facilitated a talk in Cambridge by Black Power advocate H. Rap Brown. The incendiary speech coincided with an outbreak of rioting, arson and shootings.

Memories of the 1960s maelstrom did not completely subside over the decades, and integration came slowly. Dorchester County elected its first Black commissioner in 1986, and Cambridge elected its first Black mayor in 2008.

That year, Ms. Richardson was feted by the political establishment. She received a key to the city, and a street in Cambridge was named in her honor. Other proclamations and resolutions were passed by local, state and federal officials. “This is really overwhelming,” she said, considering that many earlier holders of those offices “were ready to run us out of town back then.”

Matt Schudel and Harrison Smith contributed to this report.