After serving in the First World War he founded a company which later evolved into Bavaria Film, and acquired the Emelka Studios in Munich.
While Bavaria went on to become a leading German production company, Ostermayr had left by the mid-1920s and worked at several other studios including the giant UFA.
Following the Second World War he entered independent production, and specialized in heimatfilm.
He was made an honorary president of the West German Film Producers' Association.
This biographical article related to film in Germany is a stub.