He attended the Accademia di Belle Arti in Florence in 1917. Although he never abandoned painting, Marini devoted himself primarily to sculpture from about 1922. From this time his work was influenced by Etruscan art and the sculpture of Arturo Martini. Marini succeeded Martini as professor at the Scuola d’Arte di Villa Reale in Monza, near Milan, in 1929, a position he retained until 1940.
During this period, Marini traveled frequently to Paris, where he associated with Massimo Campigli, Giorgio de Chirico, Alberto Magnelli, and Filippo Tibertelli de Pisis. In 1936 he moved to Tenero-Locarno, in Ticino Canton, Switzerland; during the following few years the artist often visited Zürich and Basel, where he became a friend of Alberto Giacometti, Germaine Richier, and Fritz Wotruba. In 1936, he received the Prize of the Quadriennale of Rome. In 1938, he married Mercedes Pedrazzini.
In 1940, he accepted a professorship in sculpture at the Accademia di Belle Arti di Brera (now Brera Academy) in Milan. Notable students of his include sculptor Parviz Tanavoli. In 1943, he went into exile in Switzerland, exhibiting in Basel, Bern, and Zurich. In 1946, the artist settled permanently in Milan.