Overview
The Secretary of State of His Holiness (Latin: Secretarius Status Sanctitatis Suae,
), known as the Cardinal Secretary of State, presides over the Holy See's Secretariat of State, which is the oldest and most important dicastery of the Roman Curia. The Secretariat of State performs all the political and diplomatic functions of the Holy See and the Vatican City State. The secretary of state is sometimes described as the prime minister of the Holy See, even though the nominal head of government of Vatican City is the President of the Pontifical Commission for Vatican City State.
Cardinal Pietro Parolin has been secretary of state since 2013.
Duties
The secretary of state is appointed by the Pope, and serves as one of his principal advisors. As one of the senior offices in the Roman Catholic Church, the secretary is required to be a cardinal. If the office is vacant, a non-cardinal may serve as provisional secretary of state, exercising the powers of the Secretary of State until a suitable replacement is found or the Pro-Secretary is made a cardinal in a subsequent consistory.
The secretary's term ends when the Pope who appointed him dies or leaves office. During the sede vacante period, the former secretary acts as a member of a commission with the Camerlengo of the Holy Roman Church and the former President of the Pontifical Commission for Vatican City State, which exercises some of the functions of the head of state of the Vatican City State until a new Pope is elected. Once the new Pope is chosen, the former secretary's role in the commission likewise expires, though he can be re-appointed as Secretary of State.
From Wikipedia (CC BY-SA 4.0).