Esther Cooper Jackson, whose voice for racial equality in the 1940s would elevate her into the vanguard of the civil rights revolution of the mid-20th century, died in Boston on Aug. 23, two days after her 105th birthday.

Her death, in an assisted living community, was confirmed by her daughter Kathryn Jackson. She had moved from Brooklyn to Massachusetts in 2015.

A self-proclaimed revolutionary, a vocal feminist and a member of the Communist Party in the 1940s, Ms. Jackson and her husband, James E. Jackson Jr., were among the Black radicals whose pioneering voter registration drives, union organizing efforts, opposition to police brutality and campaigns for equal rights and the desegregation of public transit, primarily in the South, provided the practical, intellectual and moral foundation for many of the legal and political gains their successors achieved in the following decades.

After she finished graduate school in 1940, Ms. Jackson became education director and executive director of the Southern Negro Youth Congress, an organization in which Black women played a leadership role, especially when men, including her husband, were away defending their country in World War II.

“Historians view the Southern Negro Youth Congress as the predecessor of the Student Nonviolent Coordinating Committee,” a major force in the civil rights movement, Michael Nash, director of the Tamiment Library at New York University, where the Jacksons’ papers are preserved, told The New York Times in 2007.