Mario Bellini studied architecture at the Milan polytechnical college until 1959. From 1961 until 1963 Bellini was director of design at the Italian department store chain La Rinascente. In 1963 Mario Bellini transferred to Olivetti, where he remained for many years as a design consultant, designing numerous calculator and typewriter models: 1965 the calculator "Programma" (1965), the pocket calculator "Divisumma" (1972), and the typewriters "Praxis 35" and "Praxis 45" (1981).
In 1972 Mario Bellini showed designs at the exhibition "Italy: The New Domestic Landscape" at the Museum of Modern Art. In 1973 Mario Bellini opened a practice in Milan. In 1978 Mario Bellini also worked as a design consultant for the carmaker Renault.
From 1986 to 1991 Mario Bellini was editor of the magazine "Domus". Mario Bellini designed numerous furnishings, lamps, and objects, including the "Amanta" (1966) sofa line for B&B Italia (1966) and "Le Bambole" (1972), seat furniture with foam-filled upholstery. For Cassina Mario Bellini desugbed"Cab" (1977), a chair with a light-weight steel frame entirely covered in leather, which was followed by other armchair and sofa models made in a similar manner. For Vitra, Mario Bellini designed several office chair models, including "Imago", "Persona", "Onda", and "Summa". Mario Bellini's seating for the German Bundestag in Berlin called "Figura", is a chair with a blue seat he also designed for Vitra. In 1990 Mario Bellini created the "Lamy Persona" fountain pen for Lamy. The other companies for whom Mario Bellini has designed lamps, electrical appliances, furniture, and utilitarian objects are Artemide, Brionvega, Bulthaupt, Erco, Flos, Minerva, Poltrona, Rosenthal, and Yamaha.
Mario Bellini was a professor of design at the Istituto Superiore del Disegno Industriale (1962-65), and has taught at the "Hochschule für angewandte Kunst" in Vienna (1982), and the Domus Academy in Milan (1986-91). Mario Bellini has also been a visiting professor abroad, notably at the Royal College of Art in London.