In 1773, at the age of twenty, Phillis accompanied Nathaniel Wheatley to London in part for her health, but also because Susanna believed she would have a better chance publishing her poetry there. She had an audience with the Lord Mayor of London (an audience with George II was arranged, but Phillis returned home beforehand), as well as with other significant members of British society, including Selina Hastings, the Countess of Huntingdon, who lent her support to Wheatley's work and allowed a volume of Wheatley's poems, published in London in 1773, to be dedicated to her. In 1774, Phillis Wheatley wrote a letter to Reverend Samson Occom, commending him on his ideas and beliefs of how the slaves should be given their natural born rights in America. Wheatley also exchanged letters with the British philanthropist John Thornton, who in turn discussed Wheatley and her poetry in his correspondence with John Newton. Along with her poetry, she was able to express her thoughts, comments and concerns to others. In 1775, Phillis Wheatley sent a copy of a poem entitled, “To His Excellency, George Washington” to him. In 1776, Washington invited Wheatley to visit him at his headquarters in Cambridge, Massachusetts, which she did in March of 1776. Thomas Paine republished the poem in the Pennsylvania Gazette in April of 1776.
In 1778, Wheatley was legally freed from slavery by her master's will. His daughter Mary Wheatley died soon afterward. Three months later, Phillis Wheatley married John Peters, a free black grocer. They struggled with poor living conditions and the deaths of two babies.
Wheatley wrote another volume of poetry but was unable to publish it because of her financial circumstances, the loss of patrons after her emancipation (often publication of books was based on gaining subscriptions for guaranteed sales beforehand), and the competition from the Revolutionary War. However, some of her poems that were to be published in that volume were later published in pamphlets and newspapers.
Her husband John Peters was imprisoned for debt in 1784, leaving an impoverished Wheatley with a sickly infant son. She went to work as a scullery maid at a boarding house to support them. The racism and sexism that marked the era had forced her into a kind of domestic labor that she had not been forced to do while her freedom was held by her masters. Wheatley died on December 5, 1784, at age 31. Her infant son died three and a half hours after her death.