While working as an editor at Verlag Georg Müller in Munich, he made the acquaintance of a number of important writers, among whom were Hans Carossa, Thomas Mann, and Rainer Maria Rilke.
To escape persecution by the Nazis, who banned his work, he immigrated in 1939 to the United Kingdom and remained there until 1951, teaching literature and art history.
At the beginning of the 20th century, Braun belonged to the movement known as Young Vienna, where he found the company of such innovative writers as Stefan Zweig, Anton Wildgans, and Max Brod.
Braun also served as secretary to the great Austrian writer Hugo von Hofmannsthal and formed a close friendship with his employer.
Braun edited and published a highly respected anthology of German lyric poetry, called Der Tausendjährige Rosenstrauch (The Thousand-Year Rose Bush), in 1937.