Born in 1909 in Milan, the son of Carlo Lazzati and his wife Angela (née Mezzanotte), as a teenager and young adult he experienced the dramatic upheavals in Italian society of the years that followed the First World War, with the violent rise to prominence of Fascism.
In 1927 Lazzati became a student in the Faculty of Classical Literature of the Catholic University of the Sacred Heart in Milan, which was under the direction of Father Agostino Gemelli, and in 1931, received his degree with the grade summa cum laude.