His first major work was the 1929 "Bohemian Musicians", performed in Vienna in 1930, and he composed music for the soundtrack of the 1932 film Ein Auto und kein Geld. Grün completed "Marlene's Wedding" and "Gaby" before being forced to leave Austria ahead of its unification with Nazi Germany. He moved to the United Kingdom in 1935, anglicising his name to "Bernard Grun". Following this, he co-composed music for the 1938 musical "Magyar Melody". On 27 March 1939, it became the first musical to be broadcast directly from a theatre and shown on television (BBC TV).