During the French and Indian War, Thomson was an opponent of the Pennsylvania proprietors' American Indian policies. He served as secretary at the Treaty of Easton and wrote An Enquiry into the Causes of the Alienation of the Delaware and Shawanese Indians from the British Interest, which blamed the war on the proprietors. He was allied with Benjamin Franklin, the leader of the anti-proprietary party, but the two men parted politically during the crisis over the Stamp Act 1765. Thomson became a leader of Philadelphia's Sons of Liberty. He was married to Hannah Harrison, daughter of prominent Quaker Richard Harrison. He was inducted into the American Philosophical Society around 1750. Thomson was a leader in the revolutionary crisis of the early 1770s. John Adams called him the "Samuel Adams of Philadelphia". Thomson served as the secretary of the Continental Congress in its entirety. Through those 15 years, the Congress saw many delegates come and go, but Thomson's dedication to recording the debates and decisions provided continuity. Along with John Hancock, the president of the Congress, Thomson's name appeared on the first published version of the Declaration of Independence in July 1776. Thomson's role as secretary to Congress was not limited to clerical duties. According to biographer Boyd Schlenther, Thomson "took a direct role in the conduct of foreign affairs." Fred S. Rolater has suggested that Thomson was essentially the "Prime Minister of the United States." Thomson is also noted for designing, with William Barton, the Great Seal of the United States, which played a prominent role in the January 14, 1784, when the Treaty of Paris was ratified. Britain's representatives in Paris initially disputed the placement of the Great Seal and Congressional President Thomas Mifflin's signature until they were mollified by Benjamin Franklin. However, Thomson's service was not without its critics. James Searle, a close friend of John Adams, and a delegate, began a cane fight on the floor of Congress against Thomson over a claim that he was misquoted in the "Minutes" that resulted in both men being slashed in the face. Such brawls on the floor were common, and many of them were promoted by argument over Thomson's recordings. Political disagreements prevented Thomson from getting a position in the new government created by the US Constitution. Thomson resigned as secretary of Congress in July 1789 and handed over the Great Seal, bringing an end to the Continental Congress. He spent his final years at Harriton House in Bryn Mawr, Pennsylvania, working on a translation of the Bible. He also published a synopsis of the four evangelists in 1815. In retirement, Thomson also pursued his interests in agricultural science and beekeeping.
Writings
As Secretary of Congress, Thomson chose what to include in the official journals of the Continental Congress. He also prepared a work of over 1000 pages that covered the political history of the American Revolution. After leaving office, he chose to destroy the work in an effort to preserve the myths of War of Independence leaders as heroes and stated that his desire to avoid "contradict all the histories of the great events of the Revolution. Let the world admire the supposed wisdom and valor of our great men. Perhaps they may adopt the qualities that have been ascribed to them, and thus good may be done. I shall not undeceive future generations." According to the publisher's note of the Historical Printing Society edition of Thomas Jefferson's Notes on the State of Virginia, edited by John Leicester Ford, Thomson contributed a 25-page appendix to the original English publication, published by John Stockdale of London in a run of approximately 200 copies. In 1853 JW Randolph and Company republished the work and incorporated various materials from the Estate provided by Jefferson's literary executor, Thomas Jefferson Randolph. The new publication corrected some errors in the original Stockdale publication, including an error in the original publication which Jefferson made note of in a 1785 missive to Thomson: "Pray ask the favor of Colo Monroe in page 5, line 17, to strike out the words 'above the mouth of the Appomattox,' which makes none sense of the passage...". The Historical Printing Society publication removes Thomson's notes from the appendix and instead offers them in footnote form throughout the work, according to the original plates to which they refer.
Later life
According to Thomas Jefferson, writing to John Adams, Thomson became senile in his old age and unable to recognize members of his own household. "Is this life?" Jefferson asked. "It is at most but the life of a cabbage; surely not worth a wish." He died on August 16, 1824. He is interred at Laurel Hill Cemetery in Philadelphia.
