According to the U.S. Department of State, the main duties of the Secretary of State are to serve as the president's adviser on foreign policy and to conduct negotiations related to foreign affairs. The office of the Secretary of State was created by Congress in 1789, and the first Secretary of State was Thomas Jefferson. According to About.com, the Secretary of State's role has remained mostly unchanged since its creation.
The U.S. Constitution lists the determination of foreign policy as the responsibility of the president. However, each elected president is permitted to appoint Cabinet members to serve as his chief advisers. The Secretary of State is one of these Cabinet members, and he or she works with the State Department and Foreign Service of the United States to carry out the president's foreign policy. It is the duty of the Secretary of State to negotiate, interpret and terminate treaties with foreign governments. He or she also informs Congress on the state of U.S. foreign relations and ensures the protection of U.S. citizens while they are abroad.
When the position of Secretary of State was created by Congress in 1789, several domestic responsibilities were also included in the role. These include holding custody of the Great Seal of the United States and the publication of certain treaties.