Matilda Electa Joselyn was born at Cicero, New York, March 24, 1826. Her parents were Dr. Hezekiah and Helen (Leslie) Joslyn. Her Father, of New England and revolutionary ancestry, was a liberal thinker and an early abolitionist, whose home was a station of the Underground Railroad, as was also her own home. From her mother, who was a member of the Leslie family of Scotland, Gage inherited her fondness for historic research.

On January 6, 1845, at the age of 18, she married Henry H. Gage, a merchant of Cicero, making their permanent home at Fayetteville, New York.

She faced prison for her actions associated with the Underground Railroad under the Fugitive Slave Law of 1850 which criminalized assistance to escaped slaves. 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.

Gage became involved in the women's rights movement in 1852 when she decided to speak at the National Women's Rights Convention in Syracuse, New York. She served as President of the National Woman Suffrage Association from 1875 to 1876, and served as either Chair of the Executive Committee or Vice President for over twenty years. 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.

Like many other Suffragists, Gage considered abortion a regrettable tragedy, although her views on the subject were more complex than simple opposition. In 1868, she wrote a letter to The Revolution (a women's rights paper edited by Elizabeth Cady Stanton and Parker Pillsbury), supporting the view that abortion was an institution supported, dominated and furthered by men. Gage opposed abortion on principle, blaming it on the 'selfish desire' of husbands to maintain their wealth by reducing their offspring:

As a result of the campaigning of the New York State Woman Suffrage Association under Gage, the state of New York granted female suffrage for electing members of the school boards. Gage ensured that every woman in her area (Fayetteville, New York) had the opportunity to vote by writing letters making them aware of their rights, and sitting at the polls making sure nobody was turned away. In 1871, Gage was part of a group of 10 women who attempted to vote. Reportedly, she stood by and argued with the polling officials on behalf of each individual woman. She supported Victoria Woodhull and (later) Ulysses S Grant in the 1872 presidential election. In 1873 she defended Susan B. Anthony when Anthony was placed on trial for having voted in that election, making compelling legal and moral arguments. In 1884, Gage was an Elector-at-Large for Belva Lockwood and the Equal Rights Party.

Gage acted as Editor of The National Citizen and Ballot Box, May 1878 - October 1881, (available on microfilm) and as Editor of The Liberal Thinker, from 1890 - onwards. These publications offered her the opportunity to publish essays and opinion pieces. The following is a partial list of published works:

Gage unsuccessfully tried to prevent the conservative takeover of the women's suffrage movement. Susan B. Anthony who had helped to found the National Woman Suffrage Association (NWSA), was primarily concerned with gaining the vote, an outlook which Gage found too narrow. Conservative Suffragists were drawn into the suffrage movement believing women's vote would achieve temperance and Christian political goals. These women were not in support of general social reform. The American Woman Suffrage Association (AWSA), part of the conservative wing of the suffrage movement (and formerly at odds with the National), was open to the prospect of merging with the NWSA under Anthony, while Anthony was working toward unifying the suffrage movement under the single goal of gaining the vote. The merger of the two organizations, pushed through by Lucy Stone, Alice Stone Blackwell and Anthony, produced the National American Woman Suffrage Association (NAWSA) in 1890. Stanton and Gage maintained their radical positions and opposed the merger of the two suffrage associations because they believed it was a threat to separation of church and state. The successful merger of the two suffrage groups prompted Gage to establish the Woman's National Liberal Union (WNLU) in 1890, of which she was President until her death (by stroke) in 1898. Attracting more radical members than NAWSA, the WNLU became the platform for radical and liberal ideas of the time. Gage became the Editor of the official journal of the WNLU, The Liberal Thinker.

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 and female property rights led to a more equal relationship between men and women. Gage spent time among the Iroquois and received the name Karonienhawi - "she who holds the sky" - upon her initiation into the Wolf Clan. She was admitted into the Iroquois Council of Matrons.

Gage died in the Baum home in Chicago, in 1898. Although Gage was cremated, there is a memorial stone at Fayetteville Cemetery that bears her slogan "There is a word sweeter than Mother, Home or Heaven. That word is Liberty." [1]

In 1993, scientific Historian Margaret W. Rossiter coined the term "Matilda effect", after Matilda Gage, to identify the social situation where woman Scientists inaccurately receive less credit for their scientific work than an objective examination of their actual effort would reveal. The "Matilda effect" is a corollary to the "Matthew effect", which was postulated by the Sociologist Robert K. Merton. Gage's legacy was detailed in biographies published by Sally Roesch Wagner, and Charlotte M. Shapiro.

The death so upset the child's aunt Maud, who had always longed for a daughter, that she required medical attention. Thomas Clarkson Gage's child was the namesake of her uncle Frank Baum's famed fictional character, Dorothy Gale. In 1996, Dr. Sally Roesch Wagner, a biographer of Matilda Joslyn Gage, located young Dorothy's grave in Bloomington. A memorial was erected in the child's memory at her gravesite on May 21, 1997. This child is often mistaken for her cousin of the same name, Dorothy Louise Gage (1883–1889), Helen Leslie (Gage) Gage's child.

Gage was well-educated and a prolific writer—the most gifted and educated woman of her age, claimed her devoted son-in-law, L. Frank Baum. She corresponded with numerous newspapers, reporting on developments in the woman suffrage movement. In 1878, she bought the Ballot Box, a 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:

Gage’s views on suffrage and feminism were considered too radical by many members of the suffrage association, and in consequence, she organized in 1890 the Woman’s National Liberal Union, whose objects were: To assert woman’s natural right to self-government; to show the cause of delay in the recognition of her demand; to preserve the principles of civil and religious liberty; to arouse public opinion to the danger of a union of church and state through an amendment to the constitution, and to denounce the doctrine of woman’s inferiority. She served as President of this union from its inception until her death in Chicago, in 1898.