Who wrote the Declaration of Independence?

Thomas Jefferson wrote the Declaration of Independence as principal author, with edits from a Committee of Five and from the full Continental Congress. On June 11, 1776 Congress appointed Jefferson, John Adams of Massachusetts, Benjamin Franklin of Pennsylvania, Roger Sherman of Connecticut, and Robert R. Livingston of New York to draft a document justifying independence in case the pending Lee resolution carried. The committee chose Jefferson, then 33 years old and the youngest member except for Livingston, to do the writing.

He drafted in his second floor rooms at the corner of Seventh and Market Streets in Philadelphia between roughly June 11 and June 28, 1776, working on a small folding desk later donated to the Smithsonian. Adams and Franklin made about 47 small changes to the draft before the committee presented it to Congress on June 28. Franklin's edits included changing "we hold these truths to be sacred and undeniable" to "we hold these truths to be self-evident," a phrase that has become the most quoted line in American political writing.

Jefferson drew on several sources. The opening philosophy of natural rights and government by consent borrowed heavily from John Locke's Second Treatise of Civil Government published in 1689 and from George Mason's Virginia Declaration of Rights drafted on June 12, 1776, just weeks before Jefferson took up his pen. The list of grievances against King George III recapitulated complaints already aired in the resolutions of the First and Second Continental Congresses. Jefferson's own preamble to the proposed Virginia Constitution provided the structural model.

From July 2 to July 4, 1776 Congress edited the draft, cutting roughly a quarter of it. The most significant deletion was a long passage attacking King George for the Atlantic slave trade, struck at the insistence of Georgia and South Carolina delegations. Jefferson resented the cuts but accepted them.

Beyond Jefferson and the committee, 56 delegates signed the engrossed parchment, beginning with John Hancock's bold signature in the center on August 2, 1776. Charles Thomson, secretary of Congress, authenticated the original printed broadside on July 4 along with Hancock. So while the answer to the question is Thomas Jefferson, the document was a collaborative work of committee, of Congress, of the philosophical traditions Jefferson drew on, and of Mason and other state level thinkers whose drafts immediately preceded it.