September 3: John Adams, Franklin, and John Jay signed the Treaty of Paris between Great Britain and the United States. November 21 and December 1: Franklin witnessed two of the first manned balloon flights, and reported on them to Sir Joseph Banks, president of the Royal Society.

March: Franklin appointed by Louis XVI to investigate F. A. Mesmer's theories of animal magnetism Franklin proposed the concept of Daylight Savings Time in the essay An Economical Project for Diminishing the Cost of Light

May 23: Franklin described his invention of bifocal glasses July 24: Franklin arrived at Southampton, England, and was visited by his son William, as well as by other friends. During his voyage, Franklin wrote "Maritime Observations," containing notes on the best form of rigging to improve the swiftness of vessels; further observations on the course, velocity, and temperature of the Gulf Stream; and a design for a sea anchor to hold ships in the wind during rough weather. September 14: Franklin arrived in Philadelphia, and was met by cannon salutes, peeling bells, and cheering crowds. October 11: Franklin elected to three-year term as a member of the Supreme Executive Council of Pennsylvania; elected President of the Council on October 18. He donated his salary to charity.

January 17: Franklin turned 80 January: Franklin designed an instrument for taking down books from high shelves.

April 23: Franklin elected President of the Pennsylvania Society for Promoting the Abolition of Slavery May 28 though September 17: Franklin served as a delegate to the constitutional convention held in Philadelphia. At its conclusion, he signed the U.S. Constitution. June 11: Franklin argued that representation to Congress should be proportional to population. July 3: Franklin proposed the "Great Compromise" on representation, making representation proportional to population in House and equal by state in Senate; approved by the Grand Committee, and enacted by the Convention on July 16. August 7 and 10: Franklin argued for extending the right to vote as widely as possible, condemning property qualification for franchise and for office-holding as unnecessary.

July 17: Franklin wrote his last will and testament, leaving the bulk of his estate to his daughter Sarah and her family; he made smaller bequests to grandsons William Temple Franklin and Benjamin Bache. Citing "the part he acted against me in the late war," Franklin left son William almost nothing.

February 12: Franklin composed, signed, and submitted the first petition against slavery to appear before the U.S. Congress November 13: Franklin observed to Jean Baptiste Le Roy in a letter that, "In this world, nothing can be said to be certain except death and taxes."

April 17: Franklin died (aged 84) and was buried in Christ Church burial ground, Fifth and Arch Streets, Philadelphia. He died quietly at home of pleurisy, accompanied by suppurated lungs.