Grün was born on 11 February 1901 in Startsch, Moravia, Austria-Hungary (now Stařeč, Czech Republic). He completed a degree in philosophy and a doctorate in law at Vienna and Prague, going on to study music theory at Vienna's national music academy under Alban Berg, Hans Gál, Felix von Weingartner, and Egon Wellesz. He composed chamber music and songs and took work as a conductor in Karlsruhe and Mannheim before joining the Comedy House (Komödienhaus) in Vienna.
His first major work was the 1929 Bohemian Musicians, performed in Vienna in 1930. He 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".
In 1946, he published his compilation The Timetables of History, adapted from Werner Stein's Kulturfahrplan, presenting human history since 5000 BC in tabular form. Each century, then decade, then year, is presented with its major events (if known) divided under the seven headings:
- Influential leaders and political events
- Literature & Theater
- Religion, Philosophy, Learning
- Visual Arts
- Scientific and technological inventions
- Daily Life, innovations, trends.
It has been in constant publication, with the most recent update in 2005.
Over the course of his life, he served as the musical director of theatres in Prague, Vienna, Berlin, and London, including His Majesty's Theatre. In addition to his own output, he was also responsible for adapting various musical works, including Bizet's Carmen, Lehár's Count of Luxembourg, Millöcker's Dubarry, and Benatzky's White Horse Inn. He married the British fashion designer Edith Hart.
Grun authored the books:
- The Timetables of History (1946)
- Private Lives of the Great Composers, Conductors, and Musical Artistes of the World (1954)
- Prince of Vienna: The Life, the Times, and the Melodies of Oscar Straus (1955)
- The Golden Quill (1956)
- Fanny Beloved (1959)
- Die Leichte Muse: Kulturgeschichte der Operette (1961)
- Aller Spass dieser Welt (1965)
- Gold und Silber: Franz Lehár und Seine Welt, translated as Gold and Silver: The Life and Times of Franz Lehár (1970)
- Alban Berg: Letters to His Wife (1971, editor and translator)
- Bernard Grun's Beste Musiker Anekdoten (1974)
- Mit Takt und Taktstock: Musikeranekdoten (1979)
Grun composed the music for over 30 musicals, including:
- Böhmische Musikanten (1929)
- Musik um Susi (1932)
- Marlenes Brautfahrt (1933)
- Die Tänzerin Fanny Elßler (1934)
- Gaby (1936)
- Balalaika (1936 musical, with George Posford)
- Madame Sans-Gêne (1937)
- Old Chelsea (1943, in part)
- Summer Song (1956 arrangement of Dvorak)
- Die Erlebnisse der Berühmten Tänzerin Fanny Elßler (1920, writer)
- An Auto and No Money (1932, composer)
- Balalaika (1939 & 1948, composer)
- Magyar Melody (1939, composer)
- White Cradle Inn (1947, released as High Fury in US; composer, arranger, & conductor)
- Brass Monkey (1948, composer)
- The Blind Goddess (1948, composer)
- Röder, Werner, Biographisches Handbuch der Deutschsprachigen Emigration nach 1933, Vol. II. (in German)
- Kornberger, Monika, "Bernhard Grün (Bernard Grun)", Oesterreichisches Musiklexikon Online, Österreichischen Akademie der Wissenschaften.
- "Bernard Grun, composer, Dies". Sarasota Herald-Tribune. 29 December 1972..
- "The Timetables of History", Books, Simon & Schuster.
- "Bernard Grun", WorldCat Identities, OCLC.
- Grun (1970).
- Traubner, Richard (2004), Operetta: A Theatrical History.
- Castle, Charles; et al. (1971), This Was Richard Tauber, p. 148.
- "Bernard Grun", Internet Movie Database.