Maria W. Stewart was born in Hartford, Connecticut, as Maria Miller. Her parents' first names and occupations are not known. Stewart was orphaned by age five and became an indentured servant, serving a clergyman until she was fifteen. She attended Connecticut Sabbath schools and read alot in the clergyman's library, teaching herself how to read and comprehend. When she was fifteen, she began supporting herself by working as a servant.
In 1826 she married James W. Stewart, taking not only his last name but also his middle initial. Her husband, a shipping agent, had served in the War of 1812 and had spent some time in England as a prisoner of war. With her marriage, she became part of Boston's small free black middle class. Stewart became involved in some of the institutions founded by that black community, including the Massachusetts General Colored Association, which worked for immediate abolition of slavery. Her husband died in 1829; the white executors of her husband’s will took the inheritance he left to his widow from her through long legal action, and she was left without funds. Black abolitionist, David Walker, had inspired Stewart and when he died six months later she went through a religious conversion in which she became convinced that God was calling her to become a "warrior" "for God and for freedom" and "for the cause of oppressed Africa."
Stewart connected with the work of abolitionist publisher William Lloyd Garrison when he advertised for writings by black women in his newspaper the Liberator. In 1831 Garrison published her first essay, Religion and the Pure Principles of Morality, as a pamphlet. (Stewart's name was misspelled as "Steward" on the initial publication. She also began public speaking, at a time when religious bans against women teaching prohibited women from speaking in public, especially to mixed audiences that included men. Frances Wright had created a public scandal by speaking in public in 1828.
In her first address, in 1832, Stewart spoke before a women-only audience at the African American Female Intelligence Society, an institution founded by the free black community of Boston. Speaking to that female black audience, she used the Bible to defend her right to speak, and spoke on both religion and justice, advocating activism for equality. The text of the talk was published in Garrison's newspaper on April 28, 1832. On September 21, 1832, Stewart delivered a second lecture, this time to an audience that also included men. She spoke at Franklin Hall, the site of the New England Anti-Slavery Society meetings. In her speech, she questioned whether free blacks were much more free than slaves, given the lack of opportunity and equality. She also questioned the move to send free blacks back to Africa. Garrison published more of her writings in The Liberator. He published the text of her speeches there, putting them into the "Ladies Department. In 1832, Garrison published a second pamphlet of her writings as Meditations from the Pen of Mrs. Maria W. Stewart. On February 27, 1833, she delivered her third public lecture, "African Rights and Liberty," at the African Masonic Hall. Her fourth and final Boston lecture before moving to New York was a "Farewell Address" on September 21, 1833, when she addressed the negative reaction that her public speaking had provoked, expressing both her dismay at having little effect, and her sense of divine call to speak publicly.
In 1835, Garrison published a pamphlet with her four speeches plus some essays and poems, titling it Productions of Mrs. Maria W. Stewart. These inspired other women to begin public speaking. In New York, Stewart remained an activist, attending the 1837 Women's Anti-slavery Convention, she supported herself teaching in public schools in Manhattan and Brooklyn, becoming an assistant to the principle of the Williamsburg School. She was also active in a black women's literary group and supported Frederick Douglass' newspaper, The North Star, but did not write for it. Stewart moved to Baltimore in 1852 or 1853, apparently after losing her teaching position in New York. There, she taught privately. In 1861, she moved to Washington, DC, where she taught school again during the Civil War. One of her new friends was Elizabeth Keckley, seamstress to First Lady Mary Todd Lincoln.
During that time Stewart was appointed to head housekeeping at the Freedman's Hospital and Asylum in the 1870s. A predecessor in this position was Sojourner Truth. The hospital had become a haven for former slaves who came to Washington. Stewart also founded a neighborhood Sunday school. In 1878, Maria Stewart discovered that a new law made her eligible for a widow's pension, for her husband's service in the Navy in the War of 1812. She used the eight dollars a month, including some retroactive payments, to republish Meditations from the Pen of Mrs. Maria W. Stewart, adding material about her life during the Civil War and also adding some letters from Garrison and others. The book was published in December 1879; on the 17th of that month, Maria W. Stewart died in the hospital in which she worked. She is buried in Washington's Graceland Cemetery.