In 1743 he was appointed surveyor of New Haven County. He moved to New Milford, Connecticut, where he became town clerk. He was accepted to the Bar in 1754, and represented New Milford in the General Assembly in 1755. He was appointed justice of the peace, and four years later justice of the Superior Court of Connecticut. He was appointed commissary to the Connecticut Troops at the start of the Revolutionary War, and was elected to the Continental Congress in 1774. He served on the committee to draft the Declaration of Independence, and served in the Congress throughout the war.
He left office in 1781, returning in 1783, serving on the committee forming the Articles of Confederation. He was a member of the Constitutional Convention in 1785, where he was a frequent speaker, helping to protect the rights of the smaller states.
He is the only person to have signed all four basic documents of American sovereignty, the Continental Association of 1774, the Declaration of Independence, the Articles of Confederation, and the United States Constitution.
He was grandfather of Roger Sherman Baldwin and William Maxwell Evarts.