Mezzasoma was born in Rome,[1] the son of middle-class Perugians; from his late teens he showed himself to be a passionate supporter of Benito Mussolini.

When Italy entered World War II as an Axis Power, he volunteered for the 7th Artillery Regiment and fought in the Western Alps against France, being awarded a Bronze Medal of Military Valor.

Unlike a great many leading figures of the government (such as Galeazzo Ciano and Dino Grandi), he stayed loyal to Mussolini long after the July 1943 Grand Council of Fascism crisis which ended the latter's rule in Rome.

He clashed with Junio Valerio Borghese and, on 19 April 1945 left for Milan, parting with his collaborators (including Giorgio Almirante).

[citation needed] Along with other fascist leaders and officials, at the end of the war he was captured near Lake Como while trying to make his way to Switzerland, and shot by the partisans in Dongo on 28 April 1945.