While attending the Academy of Fine Art in Paris, Wagner clerked at the Pathe film company, where he nurtured his interest in cinematography. He was dispatched to New York as a newsreel cameraman and, in 1919, was enlisted by Decla-Bioscop of Berlin to shoot features. Along with Karl Freund, Wagner became Germany's leading cinematographer of the 1920s and 30s, a master of the moody, Gothic lighting that characterized the expressionist movement. Among his finest achievements are Murnau's "Nosferatu" (1922) and Lang's "Spione" (1928), notable sound films include Pabst's "Westfront 1918" (1930) and "Kameradschaft" (1931) and Lang's "M" (1931).
The virtual exodus of German directors after the Nazi ascendance in 1933 deprived Wagner of vehicles equal to his talent, although he remained relatively prolific until his death in 1958.