Castello Sforzesco was formerly known as the two-winged, square-formed defensive fortress Castello di Porta Giovia, constructed with a deep moat between 1360 and 1370 by Galeazzo II Visconti, when the Visconts ruled Milan. In 1447, the local population rose in rebellion against the lords of the castle following the proclamation of the new Ambrosian Republic. During the battles, the castle was utterly destroyed; the bricks and stones were later used for the restoration of the old city wall of Milan.

Francesco Sforza, who helped Milan and the Ambrosian Republic resist the Venetian attacks, took over power in 1450 and decided to reconstruct the castle as a symbol of Milan. The newly built fortification was designed by the architect Antonio Averulino, who collaborated with such great engineers as Jacopo da Cortona and Giovanni da Milano. The result was a massive square-shaped construction with high cylindrical towers on each end of the castle. The castle was named after Francesco Sforza and became residence of the duke of Milan.

In the next centuries, the castle experienced many adversities, conquered first by the French king Louis XII and then by the Spaniards until 1525. In 1706, Milan suffered under Austrian rule until the mid-19th Century, when the united Italian state was established. Napoleon also succeeded in ruling Milan for a short time. Throughout these years, the castle served as military barracks for the Austrian troops. After Milan retained its Italian heritage, Castello Sforzesco was transformed into a civil site. The castle underwent restoration by Luca Beltrami in the 1890s, and was completed with the rebuilding of the Filarete Tower above the main entrance in 1905.

During World War II, the castle was severely damaged by bombardments, which again necessitated refurbishment, giving its present-day appearance. Today, Castello Sforzesco houses the Furniture Museum, Museum of Ancient Art, Museum of Musical Instruments, the Applied Arts Collection, Egyptian and Prehistoric sections of the Archaeological Museum, and the Achille Bertarelli Print Collection.

However, the most significant museum of the castle includes the Pinacoteca del Castello Sforzesco, which showcases Leonardo da Vinci's Codex Trivulzianus manuscript, Michelangelo's Rondanini Pietà and Andrea Mantegna's Trivulzio Madonna .