Dorothy Height, who in an 80-year campaign for social justice became the grande dame of the civil rights era and its great unsung heroine, died Tuesday morning at the age of 98.

File photo of Dorothy Irene Height. (Photo: AP) Her death was announced by the National Council of Negro Women, of which she was president emerita, and by Howard University Hospital in Washington, where she died.

In a statement, President Obama called Ms. Height “the godmother of the civil rights movement and a hero to so many Americans.”

Ms. Height is widely credited as the first person in the modern civil rights era to treat the problems of equality for women and equality for African-Americans as a seamless whole, merging concerns that had historically been largely separate.

That the American social landscape looks as it does today owes in no small part to Ms. Height. Originally trained as a social worker, she was president of the National Council of Negro Women for four decades, from 1957 to 1997, overseeing a range of programs on issues like voting rights, poverty and, in later years, AIDS.

A longtime executive of the Y.W.C.A., she presided over the integration of its facilities nationwide in the 1940s. With Gloria Steinem, Shirley Chisholm, Betty Friedan and others, she helped found the National Women’s Political Caucus in 1971.

In news coverage of the civil rights movement over the years, much was made of the so-called “Big Six” who led it: Dr. Martin Luther King Jr., James Farmer, John Lewis, A. Philip Randolph, Roy Wilkins and Whitney Young. As the only woman to work regularly alongside them on projects of national significance, Ms. Height was very much the unheralded seventh.

In 1963, Ms. Height, by then president of the National Council of Negro Women, sat on the platform an arm’s length from Dr. King as he delivered his epochal “I Have a Dream” speech. Ms. Height was one of the march’s chief organizers and a prizewinning orator herself. She was not asked to speak, however, though many other black leaders, all men, addressed the crowd that day.

If Ms. Height felt doubly stigmatized throughout her long life — pushed to the margins of women’s groups because of her race, and of black groups because of her sex — she responded with a characteristic mix of limitless energy and steely gentility to ally the two in the fight for social justice.

The recipient of the Presidential Medal of Freedom and other awards, she was accorded a place of honor on the dais on Jan. 20, 2009, when Barack Obama took the oath of office as the nation’s 44th president.

Ms. Height was the author of a memoir, “Open Wide the Freedom Gates” (PublicAffairs, 2003), with a foreword by Maya Angelou. The New York Times Book Review called the book “a poignant short course in a century of African-American history.”

Ms. Height was born in Richmond, Va. The family moved to the Pittsburgh area when she was 4. In her memoir, she recalled marching as a teenager in Times Square in an antilynching rally.

After she was accepted at Barnard College in 1929 as a star student from western Pennsylvania, she was summoned to New York to meet with the dean.

There was a problem, the dean said. That Dorothy had been admitted to Barnard, a prominent private college for women, was not in doubt. But she could not enroll — not then. Barnard had already meet its quota for Negro students that year, the dean told her.

She went on to earn bachelor’s and master’s degrees from New York University and did postgraduate work at Columbia University and the New York School of Social Work.

Ms. Height, who never married, was a longtime resident of Washington. She is survived by a sister, Anthanette Aldridge of New York City.