Rudolf Ernst entered the Akademie der Bildenden Künste ('Academy of Fine Arts') in Vienna in 1869, where he studied under August Eisenmenger (1830–1907) and Anselm Feuerbach (1829–1880). He then continued his studies in Rome. In 1874 and 1875 he travelled throughout Italy, and then went to Spain and Morocco before taking up permanent residence in Paris in 1876 (Bénézit, 2006, p. 273; Thornton, 1993, p. 80).
In Paris, he was joined a little later by the Austrian Orientalist painter Ludwig Deutsch (1855–1935), who was also a student of Feuerbach. Ernst also maintained contacts, albeit more loosely, with a few other Austrian Orientalist painters, such as Charles Wilda (1854–1907), Arthur von Ferraris (1856–1936) and Rafael Ambros (1855–1895) as well as with the Swiss Orientalist painter Rudolf Johann Weiss (1846–1933). Ernst settled in a studio in the Rue de Naval and sent his first painting to the Salon des Artistes Français in 1877 (Haja, & Wimmer, 2000, p. 226).
Ernst also visited Constantinople in the late 1880s. It is possible that he met the Ottoman archaeologist and Orientalist painter Osman Hamdi Bey (1842–1910) (Haja, & Wimmer, 2000, p. 226 and 230).
Until 1884 Ernst's artistic repertoire consisted mainly of portraits and genre scenes – charming children and musketeers – nearly always of small dimensions. From 1885, however, he limited himself to Orientalist paintings (Bénézit, 2006, p. 274; Thornton, 1993, p. 80). After travelling to Constantinople he became fascinated by the decoration of faience tiles, a technique he had learnt from the Parisian ceramicist and glassmaker Léon Fargue (1849–1909) (Haja, & Wimmer, 2000, p. 234, Bénézit, 2006, p. 274; Thornton, 1993, p. 81).
Around 1900, Ernst executed several paintings of Hindu temples, such as The Sacred Pond and The Underground Temple. Ernst rivals his compatriot Ludwig Deutsch (1855–1935) in his skilful rendering of details (Bénézit, 2006, p. 274).
In 1905, Ernst left his studio in the Rue Humboldt in Paris for Fontenay-aux-Roses, a quiet suburb at the time. He decorated his house with Islamic objects that often appeared in his paintings (Haja, & Wimmer, 2000, p. 230; Thornton, 1993, p. 81).
Ernst exhibited in Vienna and Munich and at the Salon des artistes français in Paris (Bénézit, 2006, pp. 273–274).
He received a bronze medal at the 1889 Exposition Universelle and a médaille d'honneur in 1900 (Haja, & Wimmer, 2000, p. 230).

Bénézit, E. (ed.) (2006). Ernst, Rudolf. In Dictionary of artists (Vol. 5, pp. 273-274). Paris: Gründ.

Haja, M., & Wimmer, G. (2000). Les orientalistes des écoles allemande et autrichienne. Courbevoie: ACR, pp. 226–251.

Thornton, L. (1993). Les orientalistes: peintres voyageurs, Courbevoie: ACR.