Katherine Justice's first television role was on The Big Valley in 1966. Before she even left the TV studio, she got a major part in the movie The Way West starring Kirk Douglas, Robert Mitchum, and Richard Widmark. Before the release of that movie, she was the mistress and accomplice (third billing) in the made-for-TV movie Prescription: Murder starring Peter Falk as Columbo and Gene Barry as the murderer. Her next movie role was the second female lead in 5 Card Stud with Dean Martin and Robert Mitchum starring. Dailies of her convinced Paramount Pictures to sign her for a five-year contract to make five pictures. On March 14, 1967 she was a guest star on the science fiction television series The Invaders portraying a past love in the season one episode, "The Innocents". She guest starred again in 1968 in the season two episode "The Possessed".