Wilhelm Dachauer was an Austrian painter. He studied at the Akademie der bildenden Künste in Vienna from 1899 to 1907 and was a professor at the academy from 1928 to 1944.

Dachauer was in Ried im Innkreis on 5 April 1881 into a family of clockmakers. He was intended to continue his father's business but after some struggle, he was allowed to move to Vienna, where he had a time full of privations. He started an apprenticeship as decoration painter and in the nighttime he prepared for the Academy of Applied Arts. In 1899, 17-year-old Dachauer began his studies under the supervision of Professor Griepenkerl.

In 1913, he had his first arguably successful exhibition at the Secession. He was appointed to an honored professorship of the Akademie der bildenden Künste (Academy of Fine Arts) in Vienna in 1928, a position that he occupied until 1944. Temporarily, he was rector of the institution. Among his students were Hildegard Joos, Maria Lassnig, Adalbert Pilch, and Peppino Wieternik (1919–1979).

He was one of the founders and leaders of the Federation of German Painters, Austrian branch (Bund Deutscher Maler Österreichs), which from 1937 sought to bring together painters with National Socialist sympathies. Dachauer joined the Nazi party in July 1938. A Committee of Inquiry after the end of World War 2 found him not guilty of serving the Nazis through his work, however he was never reinstated to his post at the Academy of Fine Arts.

Dachauer died in Vienna on 26 February 1951.