A volunteer in World War I, he was critical of the merger between Corradini's group and Benito Mussolini's National Fascist Party (PNF).

He was Italy's envoy to the Holy See starting 7 November 1939, and five months later to Nazi Germany, where he often met Adolf Hitler.

As the war progressed and Italy needed help, he attempted to solicit material aid from Germany, but despite assurances, little came of it.

When the war began to deteriorate for the Axis, he wrote communiques and expressed verbally to Mussolini that the Germans saw Italy simply as a buffer state from the encroaching allies and urged the Duce to seek peace with the Allies but simultaneously assured the Germans that Italy was not betraying them.

In July 1943, Alfieri was called to Rome by members of the Grand Council in order to participate in a meeting.

A member of the Grand Council of Fascism, Alfieri voted in favor of Dino Grandi's coup d'état in July 1943, that led to Mussolini's arrest and fall from power of the Italian Fascist government.