The cardinal vicar was elevated to Cardinal Bishop of Velletri-Segni on 22 March 1917, and was one of the cardinal electors in another conclave, that of 1922, resulting in the election of Pope Pius XI. In 1923, he exchanged visits with Filippo Cremonesi, a royal commissioner, who served as mayor of Rome from 1922 to 1926. Among other events, Pompili served as papal legate to the opening (24 December 1924) and closing (24 December 1925) of the holy door at the Lateran Basilica. On 9 July 1930, he was made Vice-dean of the College of Cardinals, remaining in that position until his death.