His best-known book, The Romantic Agony (1933), was a comprehensive survey of the decadent, erotic and morbid themes that characterised European authors of the late 18th and 19th centuries (see Femme fatale for a reference of one of his chapters).

Praz's only other known romantic attachment was to an Anglo-Italian woman named Perla Cacciguerra, whom he met in 1953 and called "Diamante" in the book The House of Life.

"[5] The images show the interior decor and design of Greek, Roman, Medieval, Renaissance and Victorian Homes in Europe between the period of 1770 and 1860.

The sketches, paintings, and watercolour representations capture the spatial qualities and features of the interiority and decoration of the overall space.

The images record accuracy to the shape of the room, from the carpet to the furniture, pictures, fabrics, wall colour, the hang of curtains and the placement of light.

Praz's work has documented all these interior characteristics that would have shaped the space for the residents in the eighteenth and nineteenth centuries.

[7] Through the grounding of this concept, "Praz takes the idea of the inhabiting subject, and the interior and its decoration, as pre-given concepts for the construction of this history, not ones that have emerged out of particular historical conditions",[7] thus meaning that the furniture, the home and the interior all act as a "representational evocation"[7] of the individual that resides in the home, reflecting the "character or the personality of the occupant".

The concepts and documentation style that was presented in An Illustrated History of Interior Decoration have been continued and challenged through later design writings by other critics and historians.

[8] The thorough recount of the interiority of this space "shows the apartment (in a manner of a television program), providing autobiographical accounts of associations with furnishings".

[8] This autobiographical recount chronicles architecture and orchestrates the interior, giving the reader a full account of his home and "offering us the chance to follow the true routes of privacy, and to recreate the Professor's universe, reduced to the dimensions of the human eye.

The concept of horror vacuī in art is associated with Praz, who used the term to refer to cluttered visual interior design.

While Wilson praises Praz’s work as a "masterpiece", Connolly calls The House of Life "one of the most boring books I have ever read.

In his preface of Voce dietro la scena: Un'antologia personale, Mario Praz shows his peculiar irony and understatement in reporting cases of misquotations and misinterpretations of his studies or his personality abroad.

Marie-Anne Comnène, the widow of Benjamin Crémieux, writes in Hommes et Mondes, December 1949: "There were authoritative critics: Marco Pron, Franci, Rossi, count Morra and Mademoiselle Bellonci, great animators of the Pen Club."

Charles Jackson says in The Outer Edges: "Mario Praz and Bertold Brecht make the best reading in the world for a sexual criminal."

Around 1950, Kadar Jennö translated Neoclassic Taste into Hungarian; he asserted that comrade Praz is a harsh enemy of capitalism.