The secretary of war was a member of the U.S. president's Cabinet, beginning with George Washington's administration. A similar position, called either "Secretary at War" or "Secretary of War", had been appointed to serve the Congress of the Confederation under the Articles of Confederation between 1781 and 1789. Benjamin Lincoln and later Henry Knox held the position. When Washington was inaugurated as the first President under the Constitution, he appointed Knox to continue serving as Secretary of War.

The Cabinet of the United States is the principal official advisory body to the president of the United States. The Cabinet meets with the president in a room adjacent to the Oval Office. The president chairs the meetings but is not formally a member of the Cabinet. The heads of departments, appointed by the president and confirmed by the Senate, are members of the Cabinet, and acting department heads also participate in Cabinet meetings whether or not they have been officially nominated for Senate confirmation. The president may designate heads of other agencies and non-Senate-confirmed members of the Executive Office of the President as members of the Cabinet.