Born to a career U.S. Navy officer and swimming and diving coach father (John H. Wagner) and a mother (Rudy Arnold Wagner) who was a champion skier, Wagner lived in nearly all the Continental United States with her family's various naval postings. While staying in Florida, Billy Wilder then filming Some Like It Hot saw Wagner swimming and offered her a screen test. Her parents forbade it until she finished high school. After graduating she visited Wilder, did a screen test, but turned down a role in The Apartment.
Wagner travelled the world as a fashion model then made her television debut in an episode of Wagon Train in 1959. While living in the Bahamas, she became an underwater stunt double in Sea Hunt and The Aquanauts television series. She also doubled for Joanne Dru in underwater sequences in the 1960 film September Storm. Wagner appeared on What's My Line in December 1960 as a "Stunt skindiver for television films." She married fellow underwater expert Courtney Brown who she had met whilst working on the shows.
In addition to her scuba diving and swimming, she was also a surfer.
After having a daughter named Tiffany, she later divorced Brown and became contracted to Twentieth Century Fox leading her to roles in Rio Conchos, The Green Hornet and Rosemary's Baby. She married and divorced actor James Mitchum. Wagner was also friends with Sharon Tate, with the two sharing a flat for a while.
Despite such major credits, Wagner also appeared in many lesser films such as playing an assassin named "Scuba" in Out of Sight and a photographer in Destination Inner Space, both in 1966. Wagner also appeared in several other television shows such as Perry Mason and Flipper.
Wagner lived in Malibu, but lost her home and belongings in a fire. She was active with the Malibu Historical Society.
Wagner died of cancer on February 26, 1997, aged fifty-five.