Daniels's first network television appearance came in 1952 when he portrayed the young John Quincy Adams, eldest son of John and Abigail Adams in the "Hallmark Hall of Fame" drama "A Woman for the Ages." In 1976, he reprised the role as the middle-aged and elder John Quincy Adams in the acclaimed PBS miniseries "The Adams Chronicles". He starred in the short-lived series "Captain Nice" as police chemist Carter Nash. He appeared as acid-tongued Dr. Mark Craig in "St. Elsewhere" from 1982 to 1988, for which he won two Emmy awards. Concurrently, he provided the voice of KITT in "Knight Rider" from 1982 to 1986. Daniels said in 1982, "My duties on "Knight Rider" are very simple. I do it in about an hour and a half. I've never met the cast. I haven't even met the producer."