Mongiardino was responsible for creating some of the most important and enchanting houses of the second half of twentieth century, created for an international and prestigious clientele of cultured collectors and entrepreneurs including Daylesford House in Gloucestershire for Baron Hans Heinrich Thyssen-Bornemisza, and interiors for Aristotle Onassis, Gianni Agnelli and Marella Agnelli, Lee Radziwill and Stanisław Albrecht Radziwiłł, Gianni Versace, Edmond Safra and Lily Safra, Princess Firyal of Jordan, Valentino Garavani, the Rothschild family and the Hearst family.

Also starting in the late fifties Mongiardino began his career as “production designer” in Theatre and Cinema together with Franco Zeffirelli, Peter Hall, Giancarlo Menotti and Raymond Rouleau.

In 1993, Rizzoli published “Roomscapes”, a lessons-learned monograph about Mongiardino in which revealed some of his standards of interior design, without forgetting his irreplaceable craftsmen and assistants able to transform his aesthetic dreams into reality; united to his “elective affinity that arrives after years of cooperation and in continuous exercise of affectionate understanding”.

But these works are the exception that the primary focus of Mongiardino's research, which was addressed almost exclusively to the preparation of domestic spaces, through a careful combination of the search for harmonious proportions and a love for the meticulous execution of every detail.

Skilled creator of spectacular spaces, he has been able to juxtapose ordinary objects and antiques, in a masterly game of fabrics or painted, and sculptured panels and a range of trompe-l'œil, whereby he obtained masterpieces with poor materials.