Born in Altdamm, Pomerania, (today Dąbie, district of Szczecin, Poland), Gilly was known as a prodigy and the teacher of the young Karl Friedrich Schinkel.

In the practical part, he was taught by Carl Gotthard Langhans, Michael Philipp Boumann and Baron Friedrich Wilhelm von Erdmannsdorff.

The drawings he made in France reveal his interests in architecture and reflect the intellectual climate of the Directoire.

They include views of the Fountain of Regeneration, the Rue des Colonnes—an arcaded street of baseless Doric columns leading to the Théâtre Feydeau—the chamber of the Conseil des Anciens in the Tuileries and Jean-Jacques Rousseau’s grotto in its landscaped setting at Ermenonville, Oise.

His 1797, design for the Frederick II monument reveals his debt to French neoclassicism, in particular Etienne-Louis Boullée.