Osvaldo Borsani was born in 1911 in Varedo, Italy, and studied Fine Arts at the Brera Academy, and Architecture at the Milan Polytechnic, where he graduated in 1936. During his studies, Borsani participated in the fifth edition of the Triennale with his project Casa Minima, which earned him a silver medal. He also soon began helping his father Gaetano with the family business, Atelier Varedo, designing and producing furniture with a European Art Deco influence. In 1932 the manufactory changed its name to Arredamento Borsani, and opened its first shop in Milan; during this period Borsani began to collaborate with Milanese artists such as Lucio Fontana, Agenore Fabbri, Arnaldo, and Gio Pomodoro.

In 1953 Osvaldo and his twin brother Fulgenzio founded TECNO, a company known for its technological and scientific approach to furniture production. Prominent designs produced by TECNO include the D70 sofa of 1954, which can be positioned in up to twenty different ways; the P40 chaise longue of 1955, with adjustable armrests and backrest, and movable parts; and the Graphis office system of 1968, created by Borsani and Eugenio Gerli.

In 1970, Borsani introduced the Centro Progetti Tecno, together with Marco Fantoni and his daughter Valeria, an absolutely innovative design workshop.