Congress passed the Lee Resolution declaring the colonies independent on July 2, 1776.
Richard Henry Lee of Virginia introduced the resolution in the Second Continental Congress. Its central proposal stated that the United Colonies should be free and independent states, separated from Great Britain. Congress approved that political decision on July 2.
The Declaration of Independence followed as the formal explanation of the decision. Congress adopted the declaration's final text on July 4, which is why Independence Day is celebrated on that date. John Adams believed July 2 would be remembered as the great national anniversary, but July 4 became the lasting public holiday because it was attached to the declaration's publication and wording.
The Lee Resolution did not end the Revolutionary War. Fighting continued until the Treaty of Paris in 1783. It also did not by itself provide a full explanation of the break with Britain; that was the role of the Declaration of Independence.