Indeed, il Piermarini (with the masculine definite article preceding the architect's name) serves as an occasional journalistic synonym for the celebrated opera house.

[2] With the Habsburg decision permanently to install an archduke at Milan, Piermarini was commissioned to reconstruct the ducal palace adjoining the cathedral as an appropriate city residence and to construct a wholly new country seat near Monza.

For the Royal Palace of Milan, Piermarini successfully avoided competition with the rich Gothic front of the cathedral with his sober neoclassical façade (1773–80) and created the Piazzetta Reale, as part of his urbanistic projects in the city centre.

Over the years successive internal reconstructions have altered the interior of the Teatro alla Scala, so that only Piermarini's general plan, and his facade, are what remain of his designs.

At Parabiago, his friend the successful cabinetmaker Giuseppe Maggiolini commissioned him to erect a new façade for the Chiesa Prepositurale dei Santi Gervasio e Protasio (1780).