Daniels's motion picture debut was as a school principal in the 1963 anti-war drama film "Ladybug Ladybug". In 1965, he reprised his Broadway role as a child welfare worker in the screen version of "A Thousand Clowns". In 1967 he appeared in "The Graduate" as the father of Dustin Hoffman's character. In 1969, Daniels starred as John Adams in the Broadway musical "1776"; he also appeared in the film version in 1972. Two years later, he co-starred in Richard Donner's telefilm "Sarah T. - Portrait of a Teenage Alcoholic". in 1979 he again reprised his role as the outspoken John Adams in the film "Rebels", again about the American revolution, without seeming to ever break character. He is known as the quintessential John Adams.