Weissmann graduated in law and music at Munich University, after which he studied composition and piano at the Music High School in Mannheim, as well as conducting with Max von Schillings in Berlin. He then held appointments at the opera houses in Frankfurt (1915-1916) and Stettin (1916-1917) before joining the Berlin State Opera as a conductor, working there from 1920 to 1924. During this period he began to conduct for the German Parlophon and Odéon record labels. He left his post at the Berlin State Opera in 1924 and moved first to the opera house in Münster (1924-1925), followed by that in Königsberg (1926-1927). From 1926 onwards Weissmann began to appear as a symphonic conductor, working with the Dresden Philharmonic Orchestra between 1926 and 1930 (during which period he married the distinguished soprano Meta Seinemeyer on her deathbed in 1929) and conducting the Berlin Symphony Orchestra in 1931, the Amsterdam Concertgebouw Orchestra between 1931 and 1933, and the Berlin Philharmonic Orchestra during the 1932-1933 season.