Sternefeld took private lessons with Renaat Veremans and Paul Gilson at the Royal Conservatory of Flanders in Antwerp, after which he studied conducting under Frank van der Stucken. He completed his studies at the Mozarteum in Salzburg with Bernard Paumgartner, Clemens Krauss and Herbert von Karajan. In 1938, he was appointed principal conductor of the Royal Flemish Opera. During the occupation Sternefeld, an ethnic Jew, was forced into hiding in Antwerp. In 1942, he risked his life by attending the funeral of his teacher Paul Gilson in Brussels. He was arrested in late 1943 and incarcerated in the Dossinkazerne in Mechelen. He stayed several months in this Sammellager but was released. It was during this period that he wrote his first symphony. In 1948, he left the Royal Flemish Opera for the Belgian Radio Symphony Orchestra in Brussels – serving initially as associate conductor, and then from 1957 to 1970 as principal conductor – where he became known for his interpretations of modern music.