In 1768, Wheatley wrote "To the King's Most Excellent Majesty," in which she praised King George III for repealing the Stamp Act. As the American Revolution gained strength, Wheatley's writing turned to themes that expressed ideas of the rebellious colonists.
In 1770 Wheatley wrote a poetic tribute to the evangelist George Whitefield, which received widespread acclaim. Her poetry expressed Christian themes, and many poems were dedicated to famous figures. Over one-third consist of elegies, the remainder being on religious, classical, and abstract themes. She seldom referred to her own life in her poems. One example of a poem on slavery is "On being brought from Africa to America":
- Twas mercy brought me from my Pagan land, Taught my benighted soul to understand That there's a God, that there's a Saviour too: Once I redemption neither sought nor knew. Some view our sable race with scornful eye, "Their colour is a diabolic dye." Remember, Christians, Negroes, black as Cain, May be refin'd, and join th' angelic train.
Historians have commented on her reluctance to write about slavery. Perhaps it was because she had conflicting feelings about the institution. In the poem above, critics have said that she praises slavery because it brought her to Christianity. But, in another poem, she wrote that slavery was a cruel fate.
Many white colonists found it difficult to believe that an African slave was writing excellent poetry. Wheatley had to defend her authorship of her poetry in court in 1772. She was examined by a group of Boston luminaries, including John Erving, Reverend Charles Chauncey, John Hancock, Thomas Hutchinson, the governor of Massachusetts, and his lieutenant governor Andrew Oliver. They concluded she had written the poems ascribed to her and signed an attestation, which was included in the preface of her book of collected works: Poems on Various Subjects, Religious and Moral, published in London in 1773. Publishers in Boston had declined to publish it, but her work was of great interest in London. There, Selina, Countess of Huntingdon and the Earl of Dartmouth acted as patrons to help Wheatley gain publication.
In 1778, the African-American poet Jupiter Hammon wrote an ode to Wheatley. He does not refer to himself in the poem, but by choosing Wheatley as a subject, he may have been acknowledging their common ethnicity.
Boston-based publisher and abolitionist Issac Knapp collected Wheatley's poetry along with that of enslaved North Carolina poet George Moses Horton in 1838 under the title Memoir and Poems of Phillis Wheatley, A Native African and a Slave. Also, Poems by a Slave.