The second son of painter Francesco Gai, during his youth he set up a workshop in Rome for the construction of electrostatic devices for medical use, but the company went bankrupt, forcing him to move to Genoa, where he worked in an electric motor factory and later in the merchant navy.

[1][2][3][4] In 1920, after the First World War, Gai joined the nascent Fascist movement and quickly became its leader in the Marche, where he established the first "action squads" and became regional secretary of the Italian Fasces of Combat.

In 1921 he was elected to the Italian Chamber of Deputies with the National Fascist Party, and after the March on Rome he became part of the Mussolini Cabinet as undersecretary of the Ministry of Labor, until April 1923.

[1][2][3][4] Taking into account the experience of the Spanish Civil War, in which he had participated, he designed large underground fuel tanks, sheltered from air attacks, and proposed a plan for their construction in strategic points all over the Italian territory and its colonies which, which accepted by the government but only partially implemented.

[1][2][3][4] After the armistice of Cassibile on 8 September 1943, Gai remained in northern Italy and joined the Italian Social Republic on 29 September 1943, being appointed Minister for Corporate Economy, from which however he resigned in December 1943, opposing German plans to transfer workers and machinery from Italian companies to Germany, as well the socialization of the economy supported by part of the PFR.