Early career 
Born into a middle-class family, he joined the priesthood after completing his studies and, although he was defrocked in 1911, he remained a lifelong adherent of conservative Catholicism. He then followed a career in journalism, founding the Vita Italian all'estero as a magazine for emigrants. This was followed by his journal La Vita Italiana, which was noted for its antisemitism in the run-up to World War I. He soon became involved in right-wing politics, eventually becoming a member of Benito Mussolini's fascists and taking part in the March on Rome.
Preziosi was not initially an anti-Semite but after Italy's poor returns for the involvement in the First World War he came to blame the Jews for the country's ills. He accused the Jews of being incapable of being fully Italian due to their "double loyalties" and the growth of Zionism and believed in the notions of a conspiracy between the Jews, communism, Freemasonry, capitalism and democracy. Much of his thought was derived from La Libre Parole, a newspaper founded by Edouard Drumont, Howell Arthur Gwynne's The Cause of World Unrest and The Dearborn Independent of Henry Ford. He became the first to translate The Protocols of the Elders of Zion into Italian in 1921. Such was the strength of his conviction that Preziosi even attacked fellow anti-Semtie Paolo Orano for his 'soft' stance on Jews.
Initially, although a hardliner in terms of his fascism, he denounced Nazism as parochial, exclusionary and responsible for pushing Europe towards communism. In fact in his early years he had demonstrated a strong Germanophobia, even producing a book entitled Germania alla Conquista dell'Italia in 1916. However from 1933 onward, he changed tack, becoming a strong advocate of close co-operation with the equally anti-Semitic Nazi Germany and occasionally criticised Italian fascism for its lack of emphasis on Judaism. His views reached a wider audience after the passing of the 1938 Racial Laws as he began to write virulently anti-Semitic articles for the national press as well as his own journal.
Preziosi also wrote "Ecco il diavolo: Israele".
Later career 
Preziosi growing prestige was rewarded in 1942 when he was made a minister of state. Following the formation of the pupper state of Italian Social Republic Preziosi was initially moved to Germany where he was to serve as Adolf Hitler's adviser on Italian affairs. Whilst in Germany he also had a show on Radio Munich, which was broadcast to Mussolini's Italy, and used it as a platform to attack the likes of Guido Buffarini Guidi and Alessandro Pavolini as "Jew lovers".
He returned to Italy in March 1944 to head up an Ispettorato Generale della Razza (General Inspectorate of Race. In this role he introduced a system based on the Nuremberg Laws and used the new code to attack the Jews. Along with fellow anti-Semite Roberto Farinacci he also became a close ally of Julius Evola during this period in a pro-Nazi alliance. Preziosi's activities were at times frustrated by Mussolini, who nursed a long-standing personal hatred for this "former priest", but Preziosi's efforts still ensured that the puppet Italian state would be involved in the Holocaust.
Following the end of the war Preziosi, rather than let himself be captured and killed by partisans (as Mussolini, Pavolini, Farinacci, and so many other RSI leaders had been), committed suicide by jumping from a high window. Some, however, have suggested that Preziosi was pushed out of the window.
- Richard S. Levy, Antisemitism: A Historical Encyclopedia of Prejudice and Persecution, Volume 2, 2005, p. 556
- Nolte, Ernst (1969). Three Faces of Fascism: Action Française, Italian fascism, National Socialism. New York: Mentor. p. 626.
- Levy, Antisemitism, p. 557
- R.J.B. Bosworth, The Oxford Handbook of Fascism, Oxford University Press, 2009, p. 299
- David D. Roberts, The Syndicalist Tradition and Italian Fascism, 1979, pp. 324-5
- Stanley G. Payne, A History of Fascism 1914-45, Routledge, 1995, p. 220
- Wiley Feinstein, The Civilization of the Holocaust in Italy: Poets, Artists, Saints, Anti-Semites, 2003, p. 200
- Ray Moseley, Mussolini: The Last 600 days of Il Duce, 2004, p. 118
- Nolte, Ernst (1969). Three Faces of Fascism: Action Française, Italian fascism, National Socialism. New York: Mentor. p. 308.
- Moseley, Mussolini, pp. 118-9
- Anthony James Gregor, Mussolini's Intellectuals: Fascist Social and Political Thought, 2004, p. 219
- A. James Gregor & Allesandro Campi, Phoenix: Fascism in Our Time, 2001, p. 175
- Aaron Gillette, Racial Theories in Fascist Italy, 2002, p. 181