Julien Guadet (1834–1908) was a French architect, theorist, and long-serving professor at the École des Beaux-Arts in Paris. In the nineteenth century the École was the leading centre of architectural education in the Western world and attracted students from across Europe and North America. Guadet himself entered the school in 1853 and trained in the ateliers of Henri Labrouste and Louis-Jules André. In 1864 he won the Grand Prix de Rome in architecture, at the time the highest state prize for an architecture student in France. The prize came with several years of funded study at the French Academy in Rome.

After his study he combined teaching responsibilities with architectural work on a relatively small number of major buildings. Early in his career he worked under Charles Garnier on the construction of the Paris Opéra (Palais Garnier), and later he designed the central post office on the Rue du Louvre (La Poste du Louvre), a characteristic Haussmannian block in Paris.

Guadet’s lasting influence, however, was above all as a teacher and theorist. From 1871 to 1894 he directed one of the three official architecture ateliers at the École des Beaux-Arts, supervising and mentoring several generations of students. In 1894 he was appointed professor of architectural theory, a post he held until his death in 1908.

Many of Guadet’s pupils went on to become prominent architects. His earlier students often worked in classical or Beaux-Arts styles, while a number of later pupils designed notable Art Nouveau buildings. His most famous student, Auguste Perret, played a major role in the design of the Théâtre des Champs-Élysées in Paris (1913), often regarded as the first building in the Art Deco style.