Born in Los Angeles, Wagner was initially a model, and at one point appeared on the entertainment program Playboy After Dark. She made her acting debut in an episode of Adam-12 in 1971. This was followed by more TV work and she also began to appear in movies, most notably The Paper Chase in which she appeared with John Houseman. Other notable appearances occurred on Marcus Welby, M.D. (in which Wagner guested as four different characters), and The Rockford Files.
According to "Bionic Beginnings", a featurette on the 2010 DVD release of The Bionic Woman's first season, it was her appearances in Paper Chase and Rockford Files that resulted in her being considered for the role of Jaime Sommers.
According to her interview in "Bionic Beginnings", Wagner never intended to reprise the role of Jaime as her contract with Universal had ended and she planned to pursue a film career (Bionic Beginnings), but she agreed when she was given some input into the development of the character, and when it was decided that Jaime would become a schoolteacher in the series.
At some point early in production of The Bionic Woman, Wagner was involved in an automobile accident that left a permanent scar on her upper lip. This scar becomes noticeable beginning with the episode "Bionic Beauty", broadcast in March 1976 (some sources, such as the Internet Movie Database, have erroneously stated that the accident occurred in 1977).
Wagner won an Emmy Award for her work as Jaime.
After The Bionic Woman ended in 1978, Wagner continued to act in film and TV, in roles ranging from the lead in a short-lived medical drama called Jessie, to appearing opposite Sylvester Stallone in Nighthawks. Arguably her best-known post-Bionic work includes her starring roles in the miniseries Scruples and Princess Daisy and the TV movie The Two Worlds of Jenny Logan. She also reunited with Lee Majors for an episode of The Fall Guy.
In 1987, 1989 and 1994, Wagner reprised the role of Jaime Sommers for a trilogy of TV-movie reunions.
More recently, she has appeared on the science fiction series Warehouse 13. She has also written books on the topic of acupressure.
Among Wagner's talents is singing, and her role in The Bionic Woman allowed her to make use of these talents on several occasions.