Son of David Gilly, he learned practice and theory with his father in Stettin (now Szczecin), and in 1788 settled in Berlin. He developed his skills while also acting as Inspector in the Royal Buildings Department aged only 16, where he worked under Erdmannsdorff and Langhans. His own designs began to experiment with stereometrically pure forms and primitivist, elemental architecture, while his studies (1794) of the medieval Marienburg (now Malbork, Poland) fortress in East Prussia led to the beginnings of a conservation programme for that Sublime building as well as to a growing appreciation of the Backsteingotik of North Germany.
In 1796 the Academy of Fine Arts, Berlin, announced a competition for a monument to King Frederick the Great (reigned 1740–86), and in 1797 Gilly's design, set in a re-ordered Leipzigerplatz, and incorporating a powerful monumental gate, sarcophagi-lids, obelisks, and a Doric temple (suggested by a design of 1786 by Hans Christian Genelli) on a massive podium, was exhibited. With this seductive image, Gilly won the admiration of younger architects and affected many of them, including von Klenze, Schinkel, Strack, and Stüler. Gilly was profoundly influenced by French theories and buildings (notably those of Bélanger), and was closely associated with his brother-in-law, Gentz, whose Mint (1798–1800) had a frieze designed by Gilly. His later unrealized designs, such as those for a National Theatre, Berlin, with its primitive Doric portico, Diocletian windows, and clearly defined bare masses, were among the most advanced of the period, influenced by Legrand and Molinos, and eventually influencing Semper in turn. His stark (also unrealized) designs for a Stonehenge-like mausoleum are unprecedented in their stripped severity. He was Professor of Optics and Perspective at the new Bauakademie (Building Academy or School of Architecture) until his untimely death.
Bothe & Reelfs (eds.) (1994);F. Gilly (1994);F. Gilly & Frick (1965);Hederer (1976a);Herrmann (1977);Horn-Oncken (1981);E. Kaufmann (1952);Middleton & Watkin (1987);Oncken (1935);Simson (1976);Watkin & Mellinghoff (1987)