Wilhelm Bernatzik was an Austrian painter.

Bernatik was the brother of the constitutional law teacher Edmund Bernatzik. Initially a law student at his father's request, he studied at the Special School for Landscape Painting at the Academy of Fine Arts, Vienna under Eduard Peithner von Lichtenfels from 1873 to 1875. In 1875, he received the Golden Füger-Medal and studied at the Kunstakademie Düsseldorf until 1878. Finally, he finished his training in Paris with Léon Bonnat. In 1880 he joined the Vienna Künstlerhaus. He painted The Vision of St Bernhard in 1882 in Heiligenkreuz Abbey, having been attracted by the mood of the Gothic place. At the 1894 World Exhibition in Antwerp, he won a medal (second class). In 1897 he was a founding member of the Vienna Secession, and served as the group's president in 1902-03. With the art critic Julius Meier-Graefe he organised a successful Impressionist exhibition in Vienna in 1903. Together with the group around Gustav Klimt, he left the Secession in 1905.

Bernatzik was primarily a landscape painter, taking motifs from Vienna and Lower Austria and preferring to paint en plein air. During his time in Paris, he absorbed Impressionist tastes. However, he also created genre paintings, including processions in landscapes and symbolic images. He was one of the art's main representatives in Vienna at the turn of the century.