By the time Franklin arrived in Philadelphia on May 5, 1775, after his second mission to Great Britain, the American Revolution had begun—with skirmishes breaking out between colonials and British at Lexington and Concord. The New England militia had forced the main British army to remain inside Boston. The Pennsylvania Assembly unanimously chose Franklin as their delegate to the Second Continental Congress. In June 1776, he was appointed a member of the Committee of Five that drafted the Declaration of Independence. Although he was temporarily disabled by gout and unable to attend most meetings of the committee, he made several "small but important" changes to the draft sent to him by Thomas Jefferson.

At the signing, he is quoted as having replied to a comment by John Hancock that they must all hang together: "Yes, we must, indeed, all hang together, or most assuredly we shall all hang separately."