After graduating Harvard and becoming pastor of King's Chapel in Boston, Freeman's revised Book of Common Prayer was adopted by the congregation.

[5][6] Though his education at Harvard had been interrupted by the American Revolutionary War, Freeman could read French, Italian, Spanish, and Portuguese and was considered a scholar.

[1][3] William Hazlitt, an English Unitarian that had traveled to the United States, soon convinced Freeman and "several respectable ministers" to cease reciting Trinitarian doxologies.

[3] On June 19, Freeman's prayer book was adopted by a 20-7 majority,[8]: 214  with three of the opposing votes coming from proprietors that had exclusively worshipped at Trinity Church since 1776.

[9]: 138 Freeman hoped that the new liturgy would have a broad appeal, writing in its preface that "no Christian, it is supposed, can take offence at, or find his conscience wounded" by the 1785 prayer book's contents.

[8]: 215  Among its critics was William White of the newly founded Episcopal Church, who disapproved of the congregation's independent prayer book adoption and its Nontrinitarian theology.

The congregation decided against approaching the Church of England to perform such an ordination due in part to its requirement that ordinands swear loyalty to the king.

However, May recalled that Freeman enjoyed a "cordial friendship" with Joseph Eckley, the latter of whose congregation at Old South Meeting House temporarily displaced to King's Chapel during renovations in 1807 or 1808.

[15] Freeman, a member of the local school committee and fellow of the American Academy of Arts and Sciences, contributed to the periodicals and collections of the Massachusetts Historical Society, which he helped found.