For many years she led the French branch of the International Abolitionist Federation, which sought to abolish state regulation of prostitution and fought trafficking in women.

Sainte-Croix wrote for La Fronde, which was founded late in 1897, as did Marguerite Durand, Séverine, Marie Bonnevial and Clémence Royer.

No doubt it was due to her husband that she was able to hold several feminist meetings in the Civil Engineers premises at 19 rue Blanche.

[2] She founded the halfway house Œuvre Libératrice (Liberating Work) in 1901 to help young women leave prostitution after their release from prison.

[5] From 1905 to 1907 Sainte-Croix was a member of the independent Coulon-Chavagnes commission that studied the marital laws in France, under which women were disadvantaged, with a view to overhauling the civil code.

[2] In 1907 she published a book entitled Le Féminisme in which she refuted the arguments of Catholics and nationalists that feminism was "un-French".

[2] Sainte-Croix attended and spoke at congresses in London, Berlin, Geneva, Rome, Kristiana (Oslo), Bucharest, Vienna, Spain and the US.

[7] By the time the States General of Feminism was held in 1931 Avril de Sainte-Croix was 76 years old, and exhausted.

[2] In 1897 Josephine Butler visited France, and a group led by Auguste de Morsier initiated re-foundation of a French branch of the International Abolitionist Federation (IAF) which campaigned for revocation of laws that regulated prostitution.

[8] Sainte-Croix and other feminists thought the regulation of prostitution was amoral in tolerating vice and enforcing a double standard of morality, and also unjust and ineffective.

[2] At the Congress on Women's Rights in 1900 she read one of the three opening reports, calling for abolition of legalized prostitution and of the double standard of morality.

[9] In March 1900 Sainte-Croix organized a banquet at the Grand Hôtel de Paris in honor of the feminist scholar Clémence Royer, whom she greatly admired.

In 1903 Sainte-Croix was secretary general of the CNFF and also of the French branch of the IAF, which she ran from her home at 1 Avenue Malakoff.

[2] In 1919 Sainte-Croix and the CNFF engaged in a campaign to convince the Allied leaders at the Versailles Peace Conference to address women and their problems in the charter of the new League of Nations, with partial success.

These congresses focused in successive years on women's legal rights, economic standing and position in the colonies.

In 1904 she attended the ICW meetings in Berlin with Marguerite Durand and Sarah Monod, where she spoke of the support the CNFF was giving to working women.

Sainte-Croix made a tour of Europe in 1924, then returned via Canada to the United States in 1925 for the sixth ICW conference in Washington, D.C.

She has belonged to the International and mixed Masonic Order Le Droit Humain which included other feminists mentioned above[13].