As a trained actor and singer he made his stage debut at the theater in Barmen in 1905. Afterwards followed engagements in Hamburg, Zürich and Dortmund among others.
At the beginning of the 20s followed again many engagements for movies.
With the outbreak of World War I Kurt Middendorf served in the army.
In the sound film era of the 30s he only got offered smallest roles and was no longer mentioned in the credits like "Abschiedswalzer" (1934).
The actor Kurt Middendorf first finished an education as a bookseller before he dedicated to the acting.
He was only able to continue his stage career after the war, this time in Berlin.