Nebel started his professional career 1909 in the field of building engineering. He took acting classes at the Lessingtheater in Berlin until 1914. His acting teachers were the famous Rudolf Blümner and Friedrich Kayssler. He wanted to give his debut at Stadttheater Haben when World War I broke out. Nebel spent the years of war on the German Eastern and Western Fronts. In 1918, during his 14-month war imprisonment in Colsterdale, England, he wrote his expressionistic poem Zuginsfeld condemning the war. In 1919, he returned to Berlin and became friends with Wassily Kandinsky, Paul Klee, Georg Muche, Kurt Schwitters, and their art. He joined the circle around Herwarth Walden and his wife Nell Walden. She initiated his collaboration at the Sturm gallery and the art school Der Sturm. Together with Hilla von Rebay und Rudolf Bauer he founded the artist group Der Krater in 1923. During this time he also worked for the magazine Der Sturm. Nebel married Hildegard Heitmeyer, the assistant of Gertrud Grunow, in 1924. He met Hildegard at the Bauhaus in Weimar. They stayed in Weimar until 1925 where they painted, wrote poems and acted. In 1933, when the National Socialists disparaged his work as degenerate art, he left Germany for Switzerland, first in Muntelier, and later in Bern. Nebel had financial problems because he was not allowed to work in Switzerland. Thanks to the effort of Kandinsky, he could regularly sell some of his paintings to the Solomon R. Guggenheim Foundation between 1936 and 1951. The German Federal Republic awarded Nebel the Order of Merit of the Federal Republic of Germany in 1965.