Jean-Baptiste-Antoine Lassus (19 March 1807 – 15 July 1857) was a French architect who became an expert in restoration or recreation of medieval architecture.

[1] Lassus submitted a plan to the Salon of 1833 for rebuilding the Tuileries Palace to return to the original design of Philibert de l'Orme.

He worked on this project for the rest of his life, concentrating on the spire and the decorations of the interior, which he restored to their earlier form.

[1] In 1843 Lassus and Eugène Viollet-le-Duc won the competition for restoration of Notre-Dame de Paris against Jean-Charles Danjoy and Jean-Jacques Arveuf.

[2] Lassus was asked to build the petit séminaire on the rue Notre-Dame des champs in 1845.

In 1848 he was asked to serve as an expert at the site of Nantes Cathedral, and was appointed diocesan architect of Chartres and Le Mans.

[5] Lassus was critical of the Académie française, which would only recognize pagan Greek and Roman architecture, which he saw as foreign imports.

[2] He believed that the buildings of the first Gothic period were rational and functional, the peak of French architecture.