Thomas Jefferson was the primary writer of the Declaration of Independence. When he was serving in the Second Continental Congress in Philadelphia, he was a young man in his early thirties. He had talent as a writer, and had many years of experience writing letters and other pieces.
In 1776, Jefferson was appointed to serve on a committee with John Adams, Benjamin Franklin, Roger Sherman, and Robert Livingston. The task given to this committee was to create a document to outline reasons for the Thirteen Colonies separating themselves from England. It was decided by the other four members of that committee that Jefferson should write the first draft of the document on his own. Two years prior, he had written a piece about the Colonies choosing whether or not to have loyalty to King George III.
After Jefferson completed the document, Adams and Franklin read over it and their added input. The final document was the Declaration of Independence.