His father, the Frankfurt gem dealer Nathan Moritz Oppenheim (1848–1933), and his mother took their life together in 1933.
In 1939, Oppenheim and his family emigrated to the US, where he worked as a private scholar in Princeton.
He and his wife Gabrielle Oppenheim-Errera hosted Sunday luncheons there for intellectuals and artists.
Albert Einstein was his great friend and they took regular Sunday morning walks together.
Oppenheim is co-founder of the so-called Hempel-Oppenheim schema (Deductive-nomological model) .