Pelletier joined freemasonry, the French Section of the Workers' International, and came to lead a feminist association.

In France, she continued to advocate for feminist and communist causes, and wrote numerous articles, essays, and literary works, even following a stroke in 1937 which made her hemiplegic.

Pelletier originally trained as an anthropologist studying the relationship between skull size and intelligence after Paul Broca with Charles Letourneau and Léonce Manouvrier.

When she left anthropology she attacked the concept of skull size as a determinant of intelligence distinguishing the sexes.

In July 1906, she and other suffragists, including Caroline Kauffmann, invaded the French Chamber of Deputies and showered down from the gallery pink slips of paper containing an appeal for the right to vote.