According to John Frankenheimer, it was Hudson's idea to have two different actors play the Arthur Hamilton/Tony Wilson role, instead of having just one actor play both parts with makeup changes like originally envisioned. Hudson felt that he would be unconvincing as Arthur Hamilton and said he would only do the movie in the Tony Wilson role. Frankenheimer agreed and felt the film was much stronger as a result of the change.
Although this film is nowadays viewed as a cult classic, European critics at the Cannes Film Festival were so hostile to the film that director John Frankenheimer refused to leave nearby Monte Carlo, where he was shooting Grand Prix (1966), for the press conference. Rock Hudson was sent instead and was unable to answer the critical questions during the hostile session.
Initially director John Frankenheimer was reluctant to cast Hudson, whom he felt was a lightweight actor in comparison to Laurence Olivier and Kirk Douglas, other actors he wanted for the lead part. It was only after Hudson's agent convinced him at a party that Hudson could do the role that he went ahead with Hudson. He has later gone on to praise Hudson's work in the film and felt he was impeccably cast.
This was John Randolph's first film for fifteen years (since an uncredited one-day bit part in "Fourteen Hours"). He had been blacklisted for his radical sympathies in the early '50s, and his wife Sara Cunningham later said that he had been on the blacklist longer than any other actor. Two other actors in prominent roles, Jeff Corey and Nedrick Young, were also long blacklisted.
"Seconds" has gained a cult status in later years and is frequently revived. According to director John Frankenheimer it's "the only movie, really, that's ever gone from failure to classic without ever having been a success."
Beach Boys composer Brian Wilson saw the movie in a theater during its first run. Overworked and showing signs of a breakdown, Wilson both liked the theme of the movie (changing identities and starting over), and found its downside disturbing. He wondered later if musical rival Phil Spector had somehow convinced Columbia Pictures to produce the movie, just "to mess with my mind".
Rock Hudson was five inches taller than his "older self" John Randolph. This was worked around with a careful choice of camera angles. Randolph and Hudson also spent casual time together in the days before shooting, so Hudson could learn to copy Randolph's mannerisms.
Although Rock Hudson is top billing, he appears on screen only after 40 minutes of running time because the character he plays has quite different face and look after being transformed by a physical reconstruction surgery. John Randolph was chosen to play the scenes of the beginning before the physical reconstruction surgery.
When Seconds was released actress Frances Reid had already been appearing for close to year on Days of Our Lives as beloved matriarch Alice Horton. A role she became very famous for and portrayed for 45 years until her death in 2010.