Prior to living in Seneca Falls, Stanton had become an admirer and friend of Lucretia Mott, the Quaker minister, feminist, and abolitionist whom she had met at the International Anti-Slavery Convention in London, England in the spring of 1840 while on her honeymoon. The two women became allies when the male delegates attending the convention voted that women should be denied participation in the proceedings, even if they, like Mott, had been nominated to serve as official delegates of their respective abolitionist societies. After considerable debate, the women were required to sit in a roped-off section hidden from the view of the men in attendance. They were soon joined by the prominent abolitionist, William Lloyd Garrison, who arrived after the vote had been taken and, in protest of the outcome, refused his seat, electing instead to sit with the women.
Mott's example and the decision to prohibit women from participating in the convention strengthened Stanton's commitment to women's rights. By 1848, her early life experiences, together with the experience in London and her initially debilitating experience as a housewife in Seneca Falls, galvanized Stanton. She later wrote:
"The general discontent I felt with woman's portion as wife, housekeeper, physician, and spiritual guide, the chaotic conditions into which everything fell without her constant supervision, and the wearied, anxious look of the majority of women, impressed me with a strong feeling that some active measures should be taken to remedy the wrongs of society in general, and of women in particular. My experience at the World Anti-slavery Convention, all I had read of the legal status of women, and the oppression I saw everywhere, together swept across my soul, intensified now by many personal experiences. It seemed as if all the elements had conspired to impel me to some onward step. I could not see what to do or where to begin -- my only thought was a public meeting for protest and discussion."
In 1848, acting on these feelings and perceptions, Stanton joined Mott, Mott's sister Martha Coffin Wright, and a handful of other women in Seneca Falls. Together they organized the first women's rights convention held in Seneca Falls on July 19 and 20. Over 300 people attended. Stanton drafted a Declaration of Sentiments, which she read at the convention. Modeled on the United States Declaration of Independence, Stanton's declaration proclaimed that men and women are created equal. She proposed, among other things, a then-controversial resolution demanding voting rights for women. The final resolutions, including female suffrage, were passed, in no small measure, because of the support of Frederick Douglass, who attended and informally spoke at the convention.
Soon after the convention, Stanton was invited to speak at a second women's rights convention in Rochester, New York, solidifying her role as an activist and reformer. Paulina Kellogg Wright Davis invited her to speak at the first National Women's Rights Convention in 1850, but because of pregnancy, Stanton chose instead to lend her name to the list of sponsors and send a speech to be read in her stead. In 1852-1853, Stanton was introduced to Susan B. Anthony on a street in Seneca Falls by Amelia Bloomer, a feminist and mutual acquaintance who had not signed the Declaration of Sentiments and subsequent resolutions despite her attendance at the Seneca Falls convention.
Although best known for their joint work on behalf of women's suffrage, Stanton and Anthony first joined the temperance movement. Together, they were instrumental in founding the short-lived Woman's State Temperance Society (1852-1853). During her presidency of the organization, Stanton scandalized many supporters by suggesting that drunkenness be made sufficient cause for divorce. Stanton and Anthony's focus, however, soon shifted to female suffrage and women's rights.
Single and having no children, Anthony had the time and energy to do the speaking and traveling that Stanton was unable to do. Their skills complemented each other; Stanton,
the better orator and writer, scripted many of Anthony's speeches, while Anthony was the movement's organizer and tactician. Writing a tribute that appeared in the New York Times when Stanton died, Anthony described Stanton as having "forged the thunderbolts" that she (Anthony) "fired." Unlike Anthony's relatively narrow focus on suffrage, Stanton wanted to push for a broader platform of women's rights in general. While their opposing viewpoints led to some discussion and conflict, no disagreement threatened their friendship or working relationship; the two women remained close friends and colleagues until Stanton's death some 50 years after their initial meeting.
While always recognized as movement leaders whose support was sought, Stanton and Anthony's voices were soon joined by others who began assuming leadership positions within the movement. These women included, among others, Matilda Joslyn Gage.