In politics, Mayhew bitterly opposed the Stamp Act, and urged the necessity of colonial union to secure colonial liberties. He was famous, in part, for his 1750 and 1754 election sermons espousing American rights — the cause of liberty and the right and duty to resist tyranny; other famous sermons included "The Snare Broken," 1766. His sermons and writings were a powerful influence in the development of the movement for liberty and independence. The extent of his political feeling can be seen in his , a sermon delivered on the 100th anniversary of the execution of Charles I. Taking vigorous issue with recent efforts to portray Charles as a martyred monarch, Mayhew began with observations on the antiquity of English liberties. The English constitution, he asserted, “is originally and essentially free.” Roman sources, such as the reliable Tacitus, made it clear that “the ancient Britons … were extremely jealous of their liberties.” England’s monarchs originally held their throne “solely by grant of parliament,” so the ancient English kings ruled “by the voluntary consent of the people.” After forty pages of such historical discourse, Mayhew reached his major point: the essential rightness of the execution of an English king when he too greatly infringed upon British liberties. The vigor of Mayhew’s sermon established his reputation. It was published not only in Boston, but also in London in 1752 and again in 1767. In Boston, John Adams remembered long afterward that Mayhew’s sermon, “was read by everybody.” Some would say later that this sermon was the first volley of the American Revolution, setting forth the intellectual and scriptural justification for rebellion against the Crown. In 1763 he turned his attention to the Society for the Propagation of the Gospel, a branch of the Church of England established "to send priests and schoolteachers to America to help provide the Church's ministry to the colonists". His Observations on the Charter and Conduct of the Society for the Propagation of the Gospel in Foreign Parts was published in Boston and London and raised considerable opposition in England and America; Thomas Secker, then archbishop of Canterbury, wrote an Answer the following year. In 1765, with the provocation of the Stamp Act fresh, Mayhew delivered another rousing sermon on the virtues of liberty and the iniquity of tyranny. The essence of slavery, he announced, consists in subjection to others—“whether many, few, or but one, it matters not.” The day after his sermon, a Boston mob attacked Chief Justice Thomas Hutchinson’s house, and many thought Mayhew was responsible. Mayhew was Dudleian lecturer at Harvard in 1765. He died July 1766. A quarter century after his death, the following lines were delivered at the Harvard commencement address of 1792: While Britain claim'd by laws our rights to lead, And faith was fetter'd by a bigot's creed. Then mental freedom first her power display'd and call'd a MAYHEW to religion's aid. For this great truth, he boldly led the van, That private judgment was the right of man.
