For approximately six more years, Kelley lived with her parents in Massachusetts and taught at small local schools. Then in 1836, she moved to Lynn, Massachusetts, where she taught at a local school and came into contact with fellow Quakers who preached the ideas of dietary restriction, temperance, pacifism, and antislavery. She thus became interested in the health theories of Sylvester Graham and gained a general interest in the abolition of slavery after hearing William Lloyd Garrison, editor of the abolitionist publication The Liberator, lecture. As a result, Kelley joined the Female Anti-Slavery Society of Lynn and was soon elected to a committee charged with collecting signatures for petitions to the Federal government to end slavery in the District of Columbia. Kelley passionately carried out her assignment, and in 1837 she collected the signatures of nearly half the women of Lynn.
Abby Kelley was also a member of the Quaker Meeting at the "Friends Meeting House" in Uxbridge, Massachusetts. The Quakers in early Uxbridge were abolitionists who had originated from Smithfield, Rhode Island and who built "the Old Brick" Meetinghouse circa 1770. One notation reports that she was disowned by the Uxbridge Meeting for anti-slavery lecturing. There are references to the Underground railroad having had a significant pressence in south Uxbridge, near the Meeting house, and in the Blackstone Valley, and of Abby Kelley's involvement.
Abby’s views became progressively more radical as she worked with abolitionists such as Angelina Grimke. She became an “ultra”, advocating not only the abolition of slavery, but also full civil equality for blacks. In addition, the influence of William Lloyd Garrison led her to adopt the position of “non-resistance," which went beyond opposing war to opposing all forms of government coercion. Radical abolitionists led by Garrison refused to serve on juries, join the military, or vote. The Garrisonian call for the end of slavery and the extension of civil rights to women and African Americans caused further controversy. Abby’s advocacy of the radical abolitionist movement eventually earned her the pejorative label of a “Jezebel.” Meanwhile, many of her fellow abolitionists praised her public speaking skills and her dedication to the cause. The overall influence of Kelley’s work was illustrated as women who claimed ideological progeny in their activism were called “Abby Kelleyites,” and radical abolitionism became known as “Abby Kelleyism.”
Following the Panic of 1837, Abby Kelley took charge of fundraising for the Lynn Female Society, and ended up donating a generous portion of her own money to the American Anti-Slavery Society. At the encouragement of Angelina Grimke, Abby served as the Lynn Female Society’s first delegate to the national convention of the Anti-Slavery Society in New York, where she raised her voice in discussions of fundraising, and became even more enraptured with the abolitionist cause with the drafting of the Society’s declaration. This convention served as a springboard from which Kelley leapt into her work in the Anti-Slavery Society, distributing petitions, fundraising, and attending conferences.
In 1838, Kelley became further involved with the political activism of the Anti-Slavery society by giving her first public speech to a “promiscuous” (mixed gender) audience at the women’s anti-slavery convention in Philadelphia. Despite vociferous protesters, Kelley eloquently proclaimed the doctrine of abolitionism. In the following months, she further established herself as a public figure by speaking to more mixed gender crowds, such as that at the New England Anti-Slavery Convention where she also stood on a committee composed of both genders. Thus, by 1839, Kelley was fully entrenched in the Anti-Slavery Society, and continued her activism in the Society, while still acknowledging Quaker tradition by refusing payment for her efforts.
In the following years, Abby Kelley maintained a noteworthy position in the Anti-Slavery Society as a lecturer and fundraiser. Although she encountered constant objections to her public activism as a woman working closely with and presenting public lectures to men, Abby continued her work without faltering or complaining. She often shared her platform with ex-slaves despite the additional scorn this entailed. "I rejoice to be identified with the despised people of color. If they are to be despised, so ought their advocates to be".
Although Kelley’s commitment to the Anti-Slavery Society was evident, many male members objected to the ideas propounded by Garrison, Kelley, and other radicals. As a result, when Abby Kelley was elected to the national business committee of the Anti-Slavery Society, the conservative members of the Society left in protest, and the two sects of abolitionists officially severed. Thus, the Society was left in the hands of pacifist radical abolitionists in favor of complete egalitarianism, which should be obtained without the aid of any government, as all such institutions were constructed on the violence of war. In 1854 Abby became the Anti-Slavery Society’s chief fundraiser and general financial agent, and in 1857 she took the position of general agent in charge of lecture and convention schedules.
Fighting for women’s rights soon became a new priority for many ultra abolitionists. In her time in public life, Abby influenced future suffragettes such as Susan B. Anthony and Lucy Stone by encouraging them to take on a role in political activism. Abby helped organize and was a key speaker at the first national woman’s rights convention in Worcester, Massachusetts in 1850 (The better known Seneca Falls convention, held in 1848, was not national). A fictionalized version of her role in the convention was included in the play “Angels and Infidels” performed in Worcester on the 150th anniversary of the convention. Around the time of this convention, Kelley wrote to a friend, from where she was staying in Duchess County, New York, and told of the hardships that she was facing. In that letter she wrote,... " Our cause is steady onward".
After the American Civil War, Abby chose to advocate correcting the Constitution with the 15th Amendment, while other female activists resisted any amendment that did not include women’s suffrage. She would subsequently split with Susan B. Anthony and Elizabeth Cady Stanton due to their strong opposition to the amendment. However, after the amendment passed and Garrison dissolved the Anti-Slavery Society, Abby remained active in fighting for equal rights for both African Americans and women. In 1872, Abby and her husband Stephen Symonds Foster refused to pay taxes on their jointly owned property, arguing that if Abby could not vote, then she was a victim of taxation without representation. Although their farm was consequently seized and sold, Abby continued her activism in the face of financial difficulties and poor health by writing letters to fellow radicals and other political figures until her death in 1887.
Abby continued her efforts as a lecturer and fundraiser throughout the North until in 1850, when her declining health forced her to slow her movement on the lecture trail. During her time as a lecturer, Abby married fellow abolitionist Stephen Symonds Foster in 1845 after a four year courtship. She later gave birth to their only daughter in 1847. In 1854 Abby became the Anti-Slavery Society’s chief fundraiser and general financial agent, and in 1857 she took the position of general agent in charge of lecture and convention schedules. Somehow she managed to combine motherhood and working on a farm in Worcester with her continued activism.
Despite her financial and health difficulties, Abby remained a radical activist after the end of slavery. In 1874 she and her husband risked losing their farm by refusing to pay taxes, citing "taxation without representation" because she was unable to vote.