Guillaume Trepsat became "Architect for the buildings of the crown" during the French First Empire and carried out considerable work on the restoration of the buildings and sculptures at the heart of Versailles.
Before the Revolution, Trepsat built the palace of Saint-Brice-sous-Forêt (Val d’Oise) and then the Marais theatre in Paris.
During the Consulate, he was seriously wounded in an attack on Rue Saint-Nicaise in Paris on 25 December 1799, which was directed at the First Consul, Bonaparte, and had to have a leg amputated. Bonaparte chose him to become head architect at the Hôtel des Invalides, and he later took on this role at Versailles in 1804, and then at Rambouillet the year after.
His work at Versailles comprised modest but urgent projects, in particular on the statues in the park and Colonnade Grove and the refurbishment of the Grand Trianon and Petit Trianon from 1809 to 1810.
Although somewhat excluded from the “grand project” for the palace conducted by Gondouin in 1806-1807, he nevertheless took an interest in its restoration and designed a plan for it. In 1810 he was assigned Alexandre Dufour as assistant, who took over the works on the palace. Trepsat retained a certain influence over the work on the two stables, the reservoirs and both Trianon palaces.