Miller was a basketball star at UCLA, where his father was a physical education instructor. In his senior year, while working as a furniture mover to pay for school, he was discovered on Sunset Boulevard by a Hollywood agent who signed him with MGM. He became the first blond Tarzan in Tarzan, the Ape Man (1959), a cheapie/quickie which lifted most of its footage from earlier Johnny Weissmuller movies. MGM had him under contract for 20 months; in that time, he worked 8 weeks as Tarzan. After that, he did guest spots on a number of TV series, finally becoming a regular on Wagon Train from 1961 to 1964 as character “Duke Shannon”. In 1965-66, he starred on NBC as the husband of Juliet Prowse in Mona McCluskey (1965).
Miller guest-starred on Gilligan's Island in 1964 as “Duke Williams” in episode “Big Man on Little Stick”, and in 1967 as “Tongo the Ape Man” in episode “Our Vines Have Tender Apes.” He would also guest-star on another Sherwood Schwartz production, The Brady Bunch, in 1973 as Carol Brady's egomaniacal high-school boyfriend "Tank Gates" in the episode "Quarterback Sneak".
He appeared as the clone (Theta-class life form) Ser 5-9 on original Battlestar Galactica series episode "The Gun On Ice Planet Zero".
He appeared as John Hays on "Hawaii 5-0" in the "Pray Love Remember, Pray Love Remember" episode in 1968. His character was a college boyfriend wrongly accused of murder.
Denny Miller later appeared as an alien invader in the television mini-series V. All together he starred in over 200 episodic television series.
He played the Gorton's Fisherman on TV ads for 14 years.
Miller wrote an autobiography titled "Didn't You Used To Be...What's His Name?" and a book about the obesity problem in the United States called "Toxic Waist?...Get To Know Sweat!". USA Book News selected this last book as a Finalist in the Health Category for "Best Books 2006".
Miller now lives with his wife, Nancy, in Las Vegas, Nevada, and teaches classes in relaxation.