Ratti's father was a silk manufacturer. He studied in Milan and at the Gregorian Univ., Rome, and was ordained in 1879. His excellence in philosophy brought him to the attention of Leo XIII. He taught in the Milan seminary, was appointed (1888) one of the college of doctors of the Ambrosian Library, Milan, and won a name for his studies in paleography. In 1907 he was made chief librarian. Called by Pius X to Rome, he became vice prefect of the Vatican Library.
In 1918, Benedict XV entrusted him with the difficult legateship in Poland. There he put the church on good terms with the new government and helped, as much as possible, the Roman Catholics of Russia. In 1919 he was made nuncio to Poland. Two years later Benedict appointed him archbishop of Milan and created him cardinal. Cardinal Ratti was elected pope eight months later (Feb. 6, 1922).