Inspired by Garrison, Child began to research slavery, using her privileges at the Boston Athenæum. The result was An Appeal in Favor of that Class of Americans Called Africans. When it was published in 1833, it was the first antislavery work published in book form in America.

"As it was the first anti-slavery work ever printed in America in book form, so I have always thought it the ablest; that is, it covered the whole ground better than an other." — Thomas Wentworth Higginson, Contemporaries, ​​​​​​​1899.

An Appeal is a comprehensive study of slavery, tracing its history from the 1400s, and offering a detailed analysis of “the true aspect of slavery” in the United States. Child presents fourteen propositions demonstrating the injustice of Southern laws, gives copious evidence of the positive effect immediate emancipation had in other nations, and refutes the claim that people of color are inferior intellectually or morally.

Child’s tone is rational and respectful, but unflinching. She skillfully weaves together a multitude of sources into a scholarly work.

Speaking directly to her fellow Northerners, Child argues that racial prejudice is even more prevalent in the North than in the South. She boldly denounces the injustice of anti-miscegenation laws and the exclusion of African Americans from public schools and transportation in Northern states.

After An Appeal was published, Child’s literary career collapsed. Her mentor and benefactor George Ticknor shunned her. The sales of her books plummeted, and she was forced to resign as editor of her children’s magazine The Juvenile Miscellany when parents withdrew subscriptions. Relying on her publications to support both herself and her husband, Child faced serious financial difficulties. She was criticized for stepping out of a woman’s sphere into the realm of politics. One prominent lawyer is said to have flung An Appeal out of his window.

Lydia Maria Child, An Appeal in Favor of that Class of Americans Called Africans, ​​​​​​​1833. Read by Maielle Merriam.

“A few weeks after the ‘Appeal’ was published, I received…[a] note from the Trustees [of the Boston Athenæum] informing me that at a recent meeting they had passed a vote to take away my privilege, lest it should prove an inconvenient precedent.” — Lydia Maria Child, to Samuel J. May, 29 Sep 1867.

“Some excellent individuals had done the brave deed of publishing books in aid of [abolition]. Among these was Mrs. Child, a lady of whom society was exceedingly proud before she published her ‘Appeal,’ and to whom society has been extremely contemptuous since.” — Harriet Martineau, The Martyr Age of the United States, ​​​​​​​1839.

"Hardly ever was there a costlier sacrifice. ... Narrow means just changing to ease; after a weary struggle, fame and social position in her grasp; every door opening before her; the sweetness of having her genius recognized. No one had supposed that independence of opinion on a moral question would wreck all this.” — Wendell Phillips, remarks at Child's funeral, 1880