If the secretary of state resigns or dies, the deputy secretary of state becomes acting secretary of state until the president nominates and the Senate confirms a replacement.

Prior to July 13, 1972, the under secretary of state had been the second ranking officer of the Department of State.

The State Department is the only federal cabinet-level agency to have two co-equal deputy secretaries.

The second deputy secretary of state, the deputy secretary of state for management and resources, serves as the "first assistant" for the purposes of the Vacancies Reform Act, but both deputy secretaries have full delegated authority to act for the secretary, if not otherwise prohibited by law.

Certain deputy secretaries of state went on to become appointed as the secretary of state, such as Lawrence Eagleburger in 1992,[1] Warren Christopher in 1993,[2] and Antony Blinken in 2021.