In 1883, he enrolled in the Istituto tecnico superiore (Politechnico) of Milan, where he studied under Camillo Boito and his assistant, Luca Beltrami.
He completed a diploma in architecture in 1887. Among his first projects was a Funeral Chapel. Brentano"s first design included two bell towers.
The next year, he moved to Venice, and won the Gori-Ferroni Competition, held in Siena, Italy, with a proposal for a classical Exhibition palace, and a medieval style church. He also won a prize for his designs for the facade of the Duomo of Milan, which had been rushed to completion in the beginnings of 19th century using plans mainly derived by Carlo Buzzi.