In the late 1960s, Parkins was linked to several men, but she insisted most of the stories were made up by gossip magazines. Some of the men included Omar Sharif, Adam West, David Hedison, and Marcel Marceau. In a 1965 interview Parkins said:

Parkins was born in Vancouver, British Columbia. At the age of 16, her adoptive mother and she moved to Los Angeles, where she enrolled at Hollywood High School and began to study acting, tap, ballet, and fencing at the Falcon School, where her mother played the piano. Her earliest employment was as a backup singer and Dancer in the nightclub acts of major stars, including Comedian George Burns. She made her film debut in a 1961 low-budget crime caper, 20,000 Eyes, and also guest-starred in a number of television series, including Leave It to Beaver, The Untouchables, Perry Mason, and The Wide Country.

She was the only female star to remain with the series through its entire run (1964–1969). In 1966, she was nominated for an Emmy Award as Best Actress in a Lead Role in a Dramatic Series, but lost to Barbara Stanwyck for The Big Valley. About losing the award on her 24th birthday, Parkins told the press:

In Peyton Place, Parkins received lead billing for her role as small-town bad girl Betty Anderson. As initially conceived, the character was scheduled to die in a car crash six weeks into the season, but audience reaction to Parkins was overwhelmingly favorable, and it was decided to keep her in the story line. In a late 1965 interview, the Actress said about her role:

After visiting London in 1968, when she served as a bridesmaid at the wedding of Valley of the Dolls co-star Sharon Tate and Director Roman Polanski, Parkins decided to move to England, where she starred in several productions. Among them: Puppet on a Chain, Shout at the Devil and The Mephisto Waltz, with Alan Alda and Jacqueline Bisset. Parkins explained why she moved to London by saying: "It's more relaxed; there's a simplicity; I love the traditions."

In the late 1970s, Parkins moved to France and married, and in the late 1980s, she adopted her only child, daughter Christina.

In the 1980s, she continued to work in television movies, including To Catch a King, in which she portrayed the Duchess of Windsor, and opposite Sharon Stone in The Calendar Girl Murders. She also auditioned for the title role in the James Bond film Octopussy (1983), but lost to Maud Adams. She returned to the role of Betty Anderson in Peyton Place: The Next Generation (1985), a one-shot sequel to her popular series.

In 1991, she starred in a Canadian mystery series entitled Scene of the Crime, then spent most of the remainder of the decade in semiretirement. She emerged in the late 1990s to participate in two Susann-inspired projects, the biography Scandalous Me and a segment of the Lifetime series Intimate Portrait. In 1995, she was chosen by Empire magazine as number 81 on their list of 100 Sexiest Stars in film history.

In 2006, she participated with Ted Casablanca on the audio commentary for the DVD release of Valley of the Dolls and attended the release party on June 13, 2006.

In Valley of the Dolls, Parkins played Anne Welles, the naive small-town girl described as "the good girl with a million-dollar face and all the bad breaks"—a character based on author Susann. The film was trashed by the critics, although Parkins was one of the few to emerge unscathed. However, the movie was a huge commercial success and eventually became a campy cult classic. "Jackie was... taken with Barbara, who she felt resembled an earlier Jackie Susann, dark and intense and with a distinctive voice."