Daniell made his feature debut in the comedy "The Awful Truth" (1929) opposite Ina Claire, then went on to appear in such classics of the 1930s as "Camille" (1934), opposite Greta Garbo, under the direction of George Cukor. In this exquisitely produced and critically well-received production, Daniell was a standout as Camille's jilted lover Baron de Varville, bringing equal measures of suavity and elegance to the role. He played the villainous Lerocle in Sam Wood's remake of the melodrama "Madame X" (1937), joined the superb ensemble in Norma Shearer's triumphant "Marie Antoinette" (1938), and had supporting roles in the Katharine Hepburn-Cary Grant remake of "Holiday" (1938; again under Cukor's direction).
Charles Chaplin tapped him for a role in his satire "The Great Dictator", and Cukor used him in the next Hepburn-Grant pairing also based on a Philip Barry property "The Philadelphia Story" (both 1940). As the 1940s progressed he was cast in such memorable movies as the Errol Flynn swashbuckler "The Sea Hawk" (1940); Joan Crawford's "A Woman's Face" (1941); the political biopic "Mission to Moscow" (1943), opposite Walter Huston; "Jane Eyre" with Orson Welles and Joan Fontaine; the fine Robert Siodmak period thriller "The Suspect" (both 1944); and the Boris Karloff-Bela Lugosi horror classic "The Body Snatcher" (1945).
Daniell remained a steady character player throughout the 1950s, showing up as a caricature of a network executive in "The Man in the Gray Flannel Suit" (1955), Vincent van Gogh's father in Vincent Minnelli's acclaimed "Lust for Life" (1956), and he made a credible solicitor in Billy Wilder's courtroom drama "Witness for the Prosecution" (1957). Other notable films featuring the deliciously icy Daniell include "Voyage to the Bottom of the Sea" (1961), "The Chapman Report" (1962), the Marlon Brando version of "Mutiny on the Bounty" (1962) as the court martial judge, and in his final screen appearance he was cast in Cukor's "My Fair Lady" (1964).