A native of Milan, Sonzogno was the son of a businessman who owned a printing plant and bookstore. When he inherited the business upon his father's death he set about turning it into a publishing house, Casa Sonzogno, which opened in 1874. The company specialized in producing cheap editions of early Italian music, and became celebrated for its one-act opera contest, which began in 1883; Pietro Mascagni's Cavalleria Rusticana, submitted in 1889 and premiering in 1890, was by far the most famous opera to win the prize.
In 1894 he established a theater, the Lirico Internazionale, in Milan. He was also one of the first publishers in Italy to launch pocket-book editions of a huge range of classical authors from all over the world, a collection he called Biblioteca Universale. The price of these minibooks (11.5 x 17.5cm) was so low, from 1 to 3.5 lire, that anybody could easily afford a personal library of classics, fiction and non-fiction.