With the rise of Nazism he left Germany for Paris and then Hollywood. Siodmak arrived in Hollywood in 1939, where he made 23 movies, many of them widely popular thrillers and crime melodramas, which critics today regard as classics of film noir.
At Universal, Siodmak made yet another B-film, Son of Dracula (1943), the third in a trilogy of Dracula movies (based on his brother Curt's original story). His second feature, and first A-film, was the Maria Montez-Jon Hall vehicle, Cobra Woman (1944), made in garish Technicolor.
But his first all-out noir was Phantom Lady (1944), for staff producer Joan Harrison, Universal's first female executive and Alfred Hitchcock's former secretary and script assistant. Following the critical success of Phantom Lady, Siodmak directed Christmas Holiday. And for the first time in Hollywood, his work attained the stylistic and thematic characteristics that are most noted in his later noirs. Christmas Holiday was then the most successful feature for star Deanna Durbin, and the one she considered her only good film. During Siodmak's tenure, Universal made the most of the noir style, but the capstone was The Killers in 1946. A critical and financial success, it earned Siodmak his only Oscar nomination for direction in Hollywood (his German production Nachts, Wenn Der Teufel Kam would be nominated for best foreign film in 1956).
He often expressed his desire to make pictures "of a different type and background" than the ones he had been making for ten years. Nevertheless, he ended his Universal contract with one last noir, the disappointing Deported (1951) which he filmed partly abroad (Siodmak was among the first refugee directors to return to Europe to make American films).
Those "different types" of films he had made -- The Great Sinner (1949) for MGM, Time Out of Mind (1947) for Universal (which Siodmak also produced), The Whistle at Eaton Falls (1951) for Columbia Pictures -- all proved ill suited to his noir sensibilities (although The Crimson Pirate, despite the difficult production, was a surprising and pleasant departure).
The five months he collaborated with Budd Schulberg on a screenplay tentatively titled A Stone in the River Hudson, which later became On the Waterfront was a major disappointment too for Siodmak. In 1954 he sued producer Sam Spiegel for copyright infringement. Siodmak was awarded $100,000, but no screen credit. To this day his contribution to the original screenplay has never been acknowledged.
He ended his career with a six-hour, two-part toga and chariot epic, Der Kampf um Rom (1968), oddly more campy (perhaps intentionally, one hopes) than Cobra Woman had been. Like the Roman Empire, it too fell, but more quickly. There was a brief and profitable foray into television in Great Britain with the O.S.S. series in the late 1950s. Siodmak was last seen publicly in an interview for Swiss television at his home in Ascona in 1971. He died alone in 1973, seven weeks after his wife's death.