Sebastian Isepp (18 February 1884 † 3 December 1954) was an Austrian painter and member of the Nötsch Circle.

After graduating from high school in Marburg in 1903, the son of an innkeeper went to the Vienna Academy of Fine Arts, where he studied with Rudolf Bacher and met Oskar Kokoschka and Egon Schiele. Stylistically, he was initially influenced by Gauguin and Symbolism, later he turned to realistically oriented painting. From 1908 to 1918 Isepp took part in important exhibitions of the Vienna Secession and was considered a leading member of the “Neukunstgruppe” alongside Kokoschka and Schiele.

During the First World War, Isepp ran the restoration workshop of the Kunsthistorisches Museum in Vienna, but from 1915 to 1918 he had to do most of his military service on the Italian front, where he was buried life-threateningly. After the end of the war and his return to Nötsch, he largely ceased his independent artistic activity. From 1921 to 1938, Vienna was again Isepp’s residence, where he first emerged as a restorer in the early 1920s, and from 1925 to 1936 he headed the restoration workshop at the Kunsthistorisches Museum in Vienna. In 1925 he married the singer Helene Hammerschlag, in 1927 their daughter Konstanze was born, in 1930 their son Martin was born.

In 1938, after the “Anschluss” of Austria, the family was forced to emigrate to London due to Helene Hammerschlag’s Jewish origins. Here Isepp, who became an English citizen in 1947, worked as a restorer at the National Gallery until his death. He also maintained friendly contact with Kokoschka in London, and in 1951 he created a portrait of Oskar Kokoschka made by Isepp.