In 1914 Nagel began acting professionally onstage. He broke into films in 1918 and soon became one of the top (and most suave) matinee idols of the silent screen. After an extremely busy career in silents, he starred in one of the first talkies, Glorious Betsy (1928); his voice and performance were impressive, and he was thereafter much in demand for sound films. He directed one film, Love Takes Flight (1937). Nagel remained intermittently busy as a screen actor until 1940, after which he appeared in only a handful of additional films. He starred on both radio and Broadway in the '40s. He was a co-founder of the Academy of Motion Picture Arts and served for a time as its president, and he was involved in the creation of the Academy Awards. Until his death he was president of the Associated Actors and Artists of America. In 1947 he was awarded a special Oscar for his work on the Motion Picture Relief Fund. He hosted the TV drama anthology series "The Silver Theater" (having long hosted its earlier radio incarnation) and was the MC of the TV quiz show "Celebrity Time."