Moretti was the son of the architect Luigi Rolland, whose most important work is the cinema-theater Adriano, and Maria Giuseppina Moretti. He studied at the Royal School of Architecture in Rome where he graduated in 1929.

In 1931 he won a three year scholarship for Roman Studies, established by the Governorate of Rome and the Royal School of Architecture. With this grant he worked with Corrado Ricci, in the arrangement of the areas east and north of Trajan's Market. He also worked as assistant for the professorships of Vincenzo Fasolo and Gustavo Giovannoni at the restoration chair.

In 1933 he met Renato Ricci, at that time president of the Opera Nazionale Balilla, that appointed Moretti ONB technical director. In this role Moretti designed some of the youth centres of Opera Nazional Balilla and Gioventu Italiana del Littorio: in 1933 in Piacenza and in Rome, Trastevere, in 1934 in Trecate, in 1935 a women centre in Piacenza and in 1937 another youth centre in Urbino.

In 1937 he took over, the design of the regulatory plan of the Foro Mussolini (renamed Foro Italico after the war), where he created some of his masterpieces, such as the Academy of fencing and the Duce's Gym (both 1936) and the commemoration cell (of 1940).

In the period between 1942 and 1945 Moretti disappeared from public view, to reappear in 1945, when arrested for his collaboration with fascism, was briefly imprisoned in the prison of San Victor, where he met count Adolfo Fossataro. After release, with him in November of the same year, founded Cofimprese company.