From the 1920s until her death she was regarded as "the grande dame of the feminist movement" in France.

Already a "liberated" woman (for the time), it was her meeting, and subsequent marriage to, Léon Brunschvicg, a feminist philosopher and member of the Ligue des droits de l'homme, that spurred her to feminist activism; she became vice-president of the League of Electors for women's suffrage.

The French Union for Women's Suffrage (UFSF: Union française pour le suffrage des femmes) was founded by a group of feminists who had attended a national congress of French feminists in Paris in 1908, led by Jeanne Schmahl and Jane Misme.

[2] The UFSF provided a less militant and more widely acceptable alternative to the Suffrage des femmes of Hubertine Auclert (1848–1914).

Cécile Brunschvicg was named Undersecretary of State for national education in the first Léon Blum government.