In 1810, at the beginning of his artistic life, he left Cologne and went to Paris, where the masterpieces of Western art acquired in Napoleon’s campaigns, which would eventually be returned to their original collections, were on display in the Musée Napoléon (now the Musée du Louvre). From 1817 onward Hittorff served as inspector of the Menus-Plaisirs du Roi, the royal institution responsible for the decoration of court festivals. His office was in a building where the decorations were put together in a seven-story-high space, like a gigantic assembly hall, resembling to a certain extent the much later Hollywood studios.
In 1818 Hittorff and his friend and colleague Jean-François-Joseph Lecointe (1783 – 1858) followed their teacher, François-Joseph Bélanger (1744 – 1818), as joint directors of the Menus-Plaisirs and architectes du roi. Hittorff was rewarded with an annual salary of thirty-five hundred francs, housing, and royalties for special commissions. Although thus successfully occupied, in 1822 he was granted an eighteen-month sabbatical to study the artistic heritage of Italy. In Sicily he researched the use of color in ancient art. A portrait by Moritz Daniel Oppenheim (1800 – 1882) shows him on site, equipped with his instruments, with the ruins of ancient Akragas (Agrigento) in the background. Behind him is the best-preserved Doric temple of Greek antiquity, known as the Temple of Concordia (mid-fifth century BCE). Visible also are the columns of the so-called Temple of Juno Lacinia. Hittorff’s arm rests on a piece of an entablature from a monumental Roman building, more fragments of which may be seen today in the Museo Archeologico Pietro Griffo in Agrigento.
Hittorff and his traveling companion, Karl Ludwig Wilhelm Zanth (1796 – 1857), exhibited their watercolors of ancient and modern Sicily in Paris, in particular during the exhibition of contemporary artists in the Salon Carré of the royal museum, the present-day Louvre. They were repeatedly rewarded with gold medals. They also published engravings serially by subscription for members of four major European royal houses: the Bourbons of France (Charles X, 1824 – 1830), the Hohenzollerns of Prussia (Frederick William III, 1797 – 1840), the Wittelsbachs of Bavaria (Louis I, 1825 – 1848), and the Bourbons of Naples and Sicily (Francis I, 1825 – 1830).
Hittorff was among the first modern scholars to recognize that Greek architecture and sculpture were originally brightly polychromed. He published his discoveries in his monumental Restitution du temple d’Empédocle à Sélinonte, ou L’architecture polychrome chez les Grecs (Paris, 1851), focusing in particular on the application of polychromy in contemporary art. He enumerated previous attempts to revive polychromy in architecture under the historical and, as he deemed it, unfavorable climatic conditions of Paris. His masterpiece of modern polychrome architecture was the church of Saint-Vincent-de-Paul in Paris, in which he incorporated large panels of lave émaillé (slabs of lava stone painted in enamel). Archaeologists’ acceptance of ancient polychromy came only at the end of his career, although specifics were and remain a subject of debate. The paintings at Saint-Vincent-de-Paul were taken down after a short time and reinstalled only in 2011.
On March 14, 1844, Hittorff accepted his nomination for membership in the National Institute in Washington, founded in 1840 with the hope of receiving the Smithson bequest and merged into the Smithsonian Institution after the latter was founded in 1846. Francis Markoe Jr. (1801 – 1872), a clerk in the diplomatic bureau of the State Department and secretary of the National Institute, conceived the project to nominate 150 French scientists and artists in preparation for the institution’s assumption of its new role, and indeed they contributed substantially to the establishment of the Smithsonian two years later. Immediately upon receiving the news of his appointment, Hittorff expressed his desire to collaborate in “the beautiful and glorious work of a strong union of two great peoples” (la belle et glorieuse oeuvre d’une forte union entre deux grands peuples). Because of their historic importance the Library of Congress preserves to this day some of Hittorff’s monumental publications bearing the stamp of the Smithsonian on their title pages.
Hittorff was thenceforth the first scholar American artists visited upon arrival in Paris. The Gare du Nord, constructed in 1859 – 1865 for Baron James de Rothschild (1792 – 1868), was his last and perhaps greatest building. Possibly because of his advanced age, Hittorff was assisted by his son Charles-Joseph (1825 – 1898) and by the second American, after Richard Morris Hunt, to study architecture in France at the École des Beaux-Arts, Henry Hobson Richardson (1838 – 1886).