 Serafini was later named Apostolic Delegate to Mexico on 4 January 1904, assessor of the Supreme Congregation of the Holy Office on 30 November 1911 and Titular Bishop of "Seleucia Pieria" on 2 March 1912.Pope Pius X created him Cardinal Priest of "Santa Cecilia in Trastevere" in the consistory of 25 May 1914.Some three months later, following Pius X's death, Serafini participated in the papal conclave to elect his successor.