The consensus of historians, based upon much documentary evidence, is that Thomas Jefferson, one of Virginia's delegates to the Continental Congress, is the author of the Declaration of Independence. Among other sources, we have Jefferson's own recollection of how the Declaration came into being:
The Committee of 5 met, no such thing as a sub-committee was proposed, but they unanimously pressed on myself alone to undertake the draught. I consented; I drew it . . . . (see link below)
Jefferson goes on to point out that both Benjamin Franklin and John Adams made several minor changes to the draft, but Jefferson must be considered the primary author. Several changes in wording occurred during the debate on the Declaration, but these did not fundamentally change Jefferson's vision of what the Declaration should accomplish.
Many of the ideas elaborated in the Declaration were clearly in Jefferson's mind two years before the drafting of the Declaration. In July, 1774, Jefferson drafted a document for the delegates of the Virginia Convention entitled A Summary View of the Rights of British America in which he argued that the colonists should address their grievances to King George:
To represent to his majesty that these his states have often individually made humble application to his imperial throne to obtain, through its intervention, some redress of their injured rights, to none of which was ever even an answer condescended.
The theme of British injuries of American interests, and the callous disregard of those injuries by the king who is supposed to protect his subjects, all of his subjects, is laid out in detail two years later in the Declaration of Independence. Even though the tone of A Summary View is, at its conclusion, conciliatory to Great Britain, the work is clearly a precursor of the Declaration in its scope and language. At the time Jefferson drafted A Summary View, war with Great Britain was a distant, almost unthinkable, possibility, and Jefferson's purpose in writing it is to attempt to convince King George and Parliament to support the Americans, not consider them enemies.
In sum, then, the Declaration, which represents the sentiments of most of the Continental Congress in 1776, is Thomas Jefferson's in thought and execution.