Some of his better-known works were written in conjunction with the composers Franz Lehár, Emmerich Kálmán, Oscar Straus, Paul Abraham, and Robert Stolz.

Following his schooling, he worked in a number of jobs, including as supernumerary, chorister, and for a theatrical agency, before turning to writing as theatre critic for a Vienna newspaper.

When he was temporarily released, the family fled to Paris, then in 1940 via Casablanca and Lisbon to New York City.

He also wrote a number of comedies, including Dancing Partner (1930), written in collaboration with Alexander Engel and produced on Broadway by David Belasco.

Grünwald died on 24 February 1951 in Forest Hills, Queens, New York City.