Hector-Martin Lefuel (Versailles, 14 November 1810 — Paris, 31 December 1880) was a French historicist architect, whose most familiar work was the completion of the Palais du Louvre, including the reconstruction of the Pavillon de Flore after a disastrous fire.
He was the son of Alexandre Henry Lefuel (1782-1850), an entrepreneurial speculative builder established in the town of Versailles, who was admitted to the École des Beaux-Arts in 1829; there he studied with Jean-Nicolas Huyot and in 1833 he received second place in the Prix de Rome competition.
A winner of the Prix de Rome in 1839, he spent the years 1840 to 1844 as a pensionary of the French Academy in Rome at the Villa Medici. On his return to France he opened his own practice and was appointed an inspector for the Chambre des députés.
Having carried out alterations as the Château de Meudon (1848) and for the housing of the Manufacture Royal de Porcelaine de Sèvres (1852), he was appointed chief architect of the Château de Fontainebleau, one of the main seats of Napoleon III and the Second French Empire; there he designed a new Imperial theatre (1853-1855). He was elected to the Académie des beaux-arts in 1855, taking the chair of Martin Gauthier. He was made a chevalier of the Legion of Honour in 1854, and a Commander of the Legion in 1857.
At the same time Lefuel was placed in charge of the ambitious project of completing the Louvre, following the murder of the architect Louis-Tullius-Joachim Visconti in 1853. Adjusting and enriching Visconti's project he completed the project, one of the showpieces of the Second Empire. Lefuel produced the Salle des États in the extended northern wing facing the Place du Palais-Royal (containing the Ministry of Finance and the library, opened in 1857, the southern extension of the Galerie du Bord de l'Eau, with the Pavillon Lesdiguères and the Pavillon Trémoille. Aiding Lefuel was the young American architect Richard Morris Hunt, who had studied under Lefuel at the École des Beaux-Arts. Following Hunt's graduation, Lefuel made Hunt inspector of the Louvre work and allowed him to design the facade of the Pavillon de la Bibliothèque.
Lefuel's work at the Pavillon de Flore which had been begun under Visconti was to the order of Napoléon III, who in 1861 authorized its remodeling. The renovation, performed between 1864 and 1868, added significant detail and sculpture to the work, which is thus noted as an example of Second Empire Neo-Baroque architecture as much as it is of the late sixteenth century. 
Lefuel also designed and erected the hôtel particulier of Achille Fould, Minister of Finance under Napoléon III, and that of the museum director Emilien de Nieuwerkerke (the Hôtel de Nieuwekerke in Parc Monceau) and the Hôtel Émonville in Abbeville.
For the Paris Exposition of 1855 he build the temporary Palais des Beaux-Arts et de l'Industrie.
His palace in Louis XIII style at Neudeck (Świerklaniec), Polish Silesia, built in 1868-72, the grandest of three residences there of the Donnersmarcks, was burnt out in 1945 and demolished in 1961.