Giuseppe Alessi studied law and was involved in Catholic Action ( Azione Cattolica ) and was co-founder in 1943 of the Italian Christian Democratic Christian Democrats. In 1944, he became president of the Comitato Nazionale di Liberation (CLN ) ( "Committee of National Liberation " ), a political body of the resistance movement, in the province of Caltanissetta. In April 1947, he became the first president of the Christian Democrats for the Region of Sicily; in May 1947 he was at the head of the first regional government of Sicily ( 1947-1949, 1955-1956 ). In 1957 he was unanimously elected President of the Regional Assembly of Sicily.
In 1963 he became a senator in the Italian Senate in Rome; He was a member of the Parliamentary Committee on Justice and the Committee to fight the Mafia. He was a deputy of the Camera dei deputati and Deputy Chairman of the Committee on Legal Affairs in 1968. Alessi led the parliamentary committee of inquiry into the events in June and July 1964, the news service Servizio Informazioni Forze Armate ( SIFAR ). From 1972 to 1992 he was president of the Istituto dell'Enciclopedia Italiana. In 1992, he retired; he became involved however for a renewal of the Christian Democrats.