Kristen was born Birgit Annalisa Rusanen in Oslo, Norway, to a Finnish mother and a German soldier father who was killed during World War II. She spent her first years in an orphanage in Norway, and was then adopted in 1949 by an American couple from Detroit, Michigan, Harold Oliver Soderquist, and Bertha, who renamed her Martha Annalise Soderquist. Her adoptive father was a professor of education at Wayne University, Detroit. Marta also has an adopted brother whom her parents adopted later.

In 1959, Kristen moved to Los Angeles, California when her father was on a sabbatical. She remained there, with a guardian, and is a graduate of Santa Monica High School.

Reflecting her Scandinavian heritage, she adopted the more European-sounding “Marta” and used Marta Kristen as her stage name. She first appeared in a 1961 episode of Alfred Hitchcock Presents, “Bang! You’re Dead”, alongside Billy Mumy, who later co-starred with Kristen in Lost in Space. Her first successful film role was that of Lorelei in the 1965 movie Beach Blanket Bingo. She later starred in Lost in Space and made numerous guest appearances on television shows. When her daughter was born in 1969, she began making television commercials and eventually appeared in more than 40. She also made the occasional film appearance in movies such as Terminal Island (1973), Once in 1974, appearing as a bare breasted ‘Humanity’, and the cult science-fiction film Battle Beyond the Stars (1980); and had a cameo role in the 1998 movie Lost in Space. She also appeared in the A&E biography Jonathan Harris, Never Fear, Smith Is Here in 2002. Kristen also provided voice work for the 2009 animated theatrical short “The Bolt Who Screwed Christmas” which also included voice work from her Lost in Space co-stars Harris, Mumy, and Angela Cartwright.

Kristen was married twice. Her first marriage was to Terry Treadwell, a psychologist, between 1964 and 1973, with whom she had a daughter named Lora Alison Treadwell. She met her second husband, Kevin P. Kane, in 1974 and they married on November 18, 1978. Her husband and she lived in Santa Monica, California, with two rescue dogs.

In May 2016, Kristen announced on her Facebook page that her husband Kevin Kane had died.