Along with Susan B. Anthony and Elizabeth Cady Stanton, Gage helped found the National Woman's Suffrage Association in 1869.

In 1878, she bought the Ballot Box, the monthly journal of a Toledo, Ohio, suffrage association, when its editor, Sarah R. L. Williams, decided to retire.

Gage turned it into The National Citizen and Ballot Box, explaining her intentions for the paper thus: Its especial object will be to secure national protection to women citizens in the exercise of their rights to vote ... it will oppose Class Legislation of whatever form ... Women of every class, condition, rank and name will find this paper their friend.Gage became its primary editor for the next three years (until 1881), writing and publishing essays on a wide range of issues.

Each edition bore the words 'The Pen Is Mightier Than The Sword', and included regular columns about prominent women in history and female inventors.

Relying on the ideas of Diodorus Siculus, an ancient Greek historian, Gage believed that goddesses began as real women who were deified because of the benefit from their inventions.

[20][full citation needed] Like her pamphlets about inventions, in Woman, Church, and State Gage argues for the presence of an ancient matriarchy that disappeared because of Christianity.

Mary Corey argues that Gage's book is the only historical monograph written by a suffragist that proposes a thesis and supports it with evidence.

[21][full citation needed] Gage's attack on the church was considered especially radical after the 1890 creation of the more conservative National American Woman Suffrage Association (NAWSA).

"[22] Even though she was beset by both financial and physical (cardiac) problems throughout her life, her work for women's rights was extensive, practical, and often brilliantly executed.

[23] Gage was considered to be more radical than either Susan B. Anthony or Elizabeth Cady Stanton (with whom she wrote History of Woman Suffrage,[24] and Declaration of the Rights of Women).

[3] During the 1876 convention, she successfully argued against a group of police who claimed the association was holding an illegal assembly; they left without pressing charges.

Conservative suffragists were drawn into the movement believing that women's vote would achieve temperance (the banning of alcohol) and Christian political goals, but not supporting more general social reform.

Despite her opposition to the Church, Gage was in her own way deeply religious, and she joined Stanton's Revising Committee to write The Woman's Bible.

She strongly supported the separation of church and state, believing "that the greatest injury to women arose from theological laws that subjugated woman to man."

She wrote in October 1881: Believing this country to be a political and not a religious organisation ... the editor of the National Citizen will use all her influence of voice and pen against "Sabbath Laws", the uses of the "Bible in School", and pre-eminently against an amendment which shall introduce "God in the Constitution"In 1893, she published Woman, Church and State, a book that outlined the variety of ways in which Christianity had oppressed women and reinforced patriarchal systems.

It was wide-ranging and built extensively upon arguments and ideas she had previously put forth in speeches (and in a chapter of History of Woman Suffrage which bore the same name).

Gage became a Theosophist, and the last two years of her life, her thoughts were concentrated upon metaphysical subjects, and the phenomena and philosophy of Spiritualism and Theosophical studies.

She had great interest in the occult mysteries of Theosophy and other Eastern speculations as to reincarnation and the illimitable creative power of humanity.

[33] Gage also strongly criticized the witch hunts that took place throughout the 1600s, interpreting them as a church-supported means of dominating and intentionally killing women.

[39] Although not historically accurate with numbers in her assertions, Gage used her interpretations of the witch hunts to denounce the Christian Church's treatment of women and advocated for justice.

Gage opposed abortion on principle, blaming it on the 'selfish desire' of husbands to maintain their wealth by reducing their offspring: The short article on "Child Murder" in your paper of March 12 that touched a subject which lies deeper down in woman's wrongs than any other.

Crummell, of 'the hidden mystery of generation, the wondrous secret of propagated life, committed to the trust of woman,' they bring up a self-evident fact of nature which needs no other inspiration, to show the world that the mother, and not the father, is the true head of the family, and that she should be able to free herself from the adulterous husband, keeping her own body a holy temple for its divine-human uses, of which as priestess and holder of the altar she alone should have control.Other feminists of the period referred to "voluntary motherhood," achieved through consensual nonprocreative sexual practices, periodic or permanent sexual abstinence, or (most importantly) the right of a woman (especially a wife) to refuse sex.

She was angered that the federal government attempted to impose citizenship upon them, thereby negating their status as a separate nation and their treaty privileges.

She wrote in 1878: That the Indians have been oppressed – are now, is true, but the United States has treaties with them, recognising them as distinct political communities, and duty towards them demands not an enforced citizenship but a faithful living up to its obligations on the part of the government.In her 1893 work, Woman, Church and State, she cited the Iroquois society, among others, as a 'matriarchate' in which women had true power, noting that a system of descent through the female line (matrilineality) and female property rights led to a more equal relationship between men and women.

[42] Gage, who lived at 210 E. Genesee St., Fayetteville, New York, for the majority of her life,[43] had five children with her husband: Charles Henry (who died in infancy), Helen Leslie, Thomas Clarkson, Julia Louise, and Maud.

Maud, by ten years the youngest of the family, initially horrified her mother when she announced her intention to marry L. Frank Baum, then merely a struggling actor with only a handful of plays to his writing credit.

However, a few minutes later, Gage started laughing, apparently realizing that her emphasis on all individuals making up their own minds was not lost on her headstrong daughter, who gave up a chance at a law career when such opportunities for women were rare.

Gage spent six months of every year with Maud and Frank, who grew to respect her greatly; his best-known works, the series beginning with The Wonderful Wizard of Oz, are thought by scholars to show her political influence.

[46] In 1996, Dr. Sally Roesch Wagner, a biographer of Matilda Joslyn Gage, located young Dorothy's grave in Bloomington.