Cardinal Jean-Louis Tauran, 71, will replace Cardinal Tarcisio Bertone after he stepped down on his 80th birthday.
The Holy Father's camerlengo is responsible for papal duties whilst there is no pope, most commonly between a pope's death and a conclave.
Cardinal Tauran will also certify that the Pope is dead and then seal his bedroom and study.
He will continue in his post as president of the Pontifical Council for Interreligious Dialogue despite his new role.
The pope also named Archbishop Giampiero Gloder, the president of the Pontifical Ecclesiastical Academy, as the new vice camerlengo.