She was born Gerda Hedwig Kronstein in Vienna, Austria on April 30, 1920, the first child of Ilona Kronstein (née Neumann, 1897, Budapest–1948, Zürich) and Robert Kronstein (1888, Vienna–1952, Vaduz), an affluent Jewish couple. Her family are originating and relating to Breslau, Berlin, Léva [hu] (German: Lewenz, Levice [sk]), Turdossin [hu] (Turdos, German: Turdoschin, Tvrdošín [sk]) (Upper Hungary), Helishoy (German: Holleschau, Holešov [cs]) (Moravia), and Reichenberg (Liberec [cs]) (Bohemia). Her father was a pharmacist, and her mother an artist, with whom Gerda, according to her autobiography, had a strained relationship as a child. As an adult, Gerda believed that her mother Ilona struggled because she did not fit in the role of a Viennese wife and mother. Gerda had a younger sister, and they attended local schools and gymnasium.

Following the 1938 Anschluss, Kronstein became involved with the anti-Nazi resistance. She and her mother were jailed that year after her father had escaped to Liechtenstein and Switzerland, where he stayed during the war. Gerda Kronstein occupied a cell for six weeks with two Christian women held on political grounds. They shared their prison food with her because Jews received restricted rations. In 1939, her mother moved to France, and Lerner’s sister relocated to Palestine. That year, Gerda immigrated to the United States under the sponsorship of the family of Bobby Jensen, her socialist fiancé.

In 1946, Gerda Lerner helped found the Los Angeles chapter of the Congress of American Women, a Communist front organization. The Lerners engaged in CPUSA activities involving trade unionism, civil rights, and anti-militarism. They suffered under the rise of McCarthyism in the 1950s, especially the Hollywood blacklist.

The Lerners returned to New York. In 1951, Gerda Lerner collaborated with poet Eve Merriam on a musical, The Singing of Women. Lerner’s novel No Farewell was published in 1955. Lerner returned to New York to study at the New School for Social Research, where she received a bachelor’s degree in 1963. She has said that her frequent status made her think about “people who did not have a voice in telling their own stories. Lerner’s insights eventually influenced her decision to earn a Ph.D. in history and then to help establish women’s history as a standard academic discipline.” In 1963, she offered the first regular college course in women’s history, which at the time had no status as a field of study in academia.

In 1966, Lerner became a founding member of the National Organization for Women (NOW), and she served as a local and national leader for a short period. In 1968, she received her first academic appointment at Sarah Lawrence College. There Lerner developed a Master of Arts Program in Women’s History, which Sarah Lawrence offered beginning in 1972; it was the first American graduate degree in the field. Lerner also taught at Long Island University in Brooklyn.

In 1979, Lerner chaired The Women’s History Institute, a fifteen-day conference (July 13–29) at Sarah Lawrence College, co-sponsored by the college, the Women’s Action Alliance, and the Smithsonian Institution. It was attended by leaders of national organizations for women and girls. When the Institute participants learned about the success of the Women’s History Week celebrated in Sonoma County, California, they decided to initiate similar commemorations within their own organizations, communities, and school districts. They also agreed to support an effort to secure a “National Women’s History Week”. This helped lead to the national establishment of Women’s History Month.

In 1980, Lerner moved to the University of Wisconsin at Madison, where she established the nation’s first Ph.D. program in women’s history. At this institution, she wrote The Creation of Patriarchy (1986), The Creation of Feminist Consciousness (1993), parts one and two of Women and History; Why History Matters (1997), and Fireweed: A Political Autobiography (2002).

From 1981 to 1982, Lerner served as president of the Organization of American Historians. As an educational director for the organization, she helped make women’s history accessible to leaders of women’s organizations and high school teachers.

Lerner died on January 2, 2013, in Madison, Wisconsin, at the age of 92. She was survived by her grown children Dan and Stephanie Lerner.