After his graduation examination in Maribor in 1903, Sebastian Isepp studied at the Academy of Fine Arts with Rudolf Bacher in Vienna. He was a member of the artist associations Hagenbund and Secession and also showed his paintings in their exhibitions. Isepp is considered the founder of the Nötsch Circle, a loose grouping of painter friends who were either born in or had moved to Nötsch and who had a significant influence on Austrian painting in the first half of the 20th century. In the First World War, Isepp fought as a soldier in the Gebirgsschützenregiment No. 1 (Mountain Troups). He did most of his war service on the Italian front, where he was nearly fatally buried. Later, his friend Hugo von Hofmannsthal would deal with this literarily in Der Schwierige. After the end of the war, Isepp was no longer active artistically, but in 1925 he began working as a restorer in the Picture Gallery of the Kunsthistorisches Museum. In 1930, together with Johannes Wilde, he founded one of the first European museum laboratories for the examination of paintings with X-rays and other analytical methods. In 1936, Isepp was appointed chief restorer. He was considered a specialist in Italian paintings. Isepp had been married to the singer Helene, née Hammerschlag, a granddaughter of the psychoanalyst Josef Breuer, since 1925. As she was considered Jewish in Nazi diction, Isepp had to emigrate with his family to Great Britain in September 1938. When he fled, he was able to take his art collection consisting of 18 paintings, 21 drawings, baroque furniture and historical lutes with him as removal goods. The art collector Antoine Seilern, whom Isepp had known since the 1920s, and Kenneth Clark, director of the National Gallery in London, arranged restoration commissions for him and so he was able to continue working as a restorer in public and private painting collections such as the National Gallery, the Ashmolean Museum in Oxford and the private collection of King George VI. For a short time, Sebastian Isepp shared a studio in London with the painter Oskar Kokoschka, who had fled from Prague to London in 1938. After 1945, Isepp worked for the Tate Gallery, the Victoria and Albert Museum, the Royal Collection and other municipal and private collections in Great Britain.