As a production manager, he in the 1920s accompanied Korda to Berlin, until in 1926 he returned to Vienna to work for his former class-mate director Gustav Ucicky.

He then experimented with other genres, for example the comedy Die Gräfin von Monte Cristo ("The Countess of Monte Cristo") (1932) with Brigitte Helm and Gustaf Gründgens, and in the same year achieved his final breakthrough with the flying drama film F.P.1 antwortet nicht written by Curt Siodmak and produced by Erich Pommer, with Conrad Veidt, Leslie Fenton and Jill Esmond.

After most of the talented directors, technicians, actors had been forced to leave in the course of the 1938 Anschluss annexation of Austria[citation needed] by Nazi Germany, Hartl became head of production for Wien-Film, the newly created body through which the UFA, and beyond it, Joseph Goebbels, controlled the Austrian film industry.

[1] Research has pointed to Hartls sophisticated use of local dialects and references to the Viennese court to subvert fascist expectations.

On 3 July 1947 he set up in Salzburg, with the support of the Creditanstalt, the film production company Neue Wiener Filmproduktionsgesellschaft.