Enrolled at the Brera Academy of Fine Arts from 1844 to 1846, Trezzini served his pictorial apprenticeship in the studio of the Induno brothers, under the guidance of Domenico, his brother-in-law, and in close contact with Gerolamo, his comrade in arms in the struggle for national liberation. He focused on military subjects and established himself as a painter of battle scenes in the 1860s. The following decade saw the introduction of anecdotal themes of a patriotic character treated in a domestic and sentimental key reflecting the models developed by the Induno brothers, the constant point of reference for all his work as a painter. He obtained a teaching post at a professional training school for young women in Milan in 1876 and was commissioned by various charitable institutions to paint portraits of their benefactors. A lithographer and illustrator, he also drew satirical cartoons for humorous journals.