On July 4, 1776, the Second Continental Congress, meeting in Philadelphia in the Pennsylvania State House (now Independence Hall), approved the Declaration of Independence. Its purpose was to set forth the principles upon which the Congress had acted two days earlier when it voted in favor of Richard Henry Lee's motion to declare the freedom and independence of the 13 American colonies from England. The Declaration was designed to influence public opinion and gain support both among the new states and abroad especially in France, from which the new "United States" sought military assistance.

Although Benjamin Franklin, John Adams, Thomas Jefferson, Roger Sherman and Robert R. Livingston comprised the committee charged with drafting the Declaration, the task fell to Jefferson, regarded as the strongest and most eloquent writer. The document is mainly his work, although the committee and Congress as a whole made a total of 86 changes to Jefferson's draft.

As a scholar well-versed in the ideas and ideals of the French and English Enlightenments, Jefferson found his greatest inspiration in the language and arguments of English philosopher John Locke, who had justified England's "Glorious Revolution" of 1688 on the basis of man's "natural rights." Locke's theory held that government was a contract between the governed and those governing, who derived their power solely from the consent of the governed and whose purpose it was to protect every man's inherent right to property, life and liberty. Jefferson's theory of "natural law" differed in that it substituted the inalienable right of "the pursuit of happiness" for "property," emphasizing that happiness is the product of civic virtue and public duty. The concept of the "pursuit of happiness" originated in the Common Sense School of Scottish philosophy, of which Lord Kames was the best-known proponent.

Jefferson emphasized the contractual justification for independence, arguing that when the tyrannical government of King George III of England repeatedly violated "natural law, " the colonists had not only the right but the duty to revolt.

The assembled Continental Congress deleted a few passages of the draft, and amended others, but outright rejected only two sections: 1) a derogatory reference to the English people; 2) a passionate denunciation of the slave trade. The latter section was left out, as Jefferson reported, to accede to the wishes of South Carolina and Georgia, who wanted to continue the importation of slaves. The rest of the draft was accepted on July 4, and 56 members of Congress began their formal signing of the document on August 2, 1776.