He developed the genre of the Viennese Film with writer Walter Reisch in the 1930s, beginning with the Franz Schubert melodrama Leise flehen meine Lieder (1933) which became an iconic role for the actor Hans Jaray and Maskerade (1934), which launched his fame as a significant director and brought Paula Wessely to international fame.

He founded his own film company, Willi Forst-Film, in 1937 and considered a move to Hollywood the same year.

Following the annexation of Austria in 1938, he was much courted by the National Socialists but succeeded in avoiding overt political statement, concentrating entirely on the opulent period musical entertainment for which he was famous and which was much in demand during World War II.

He had comparatively little success after the war except for the film The Sinner (1951) starring Hildegard Knef, which became a scandal because of the protests of the Roman Catholic church against its nudity, rare in contemporary German-speaking cinema, but which subsequently attracted an audience of seven million people.

He gave international actress Senta Berger her first role in 1957 and that same year directed his last film (Vienna, City of My Dreams), after which he retired from the industry, suggesting that his style was no longer in demand.