[2] Pettet studied with Sanford Meisner at the Neighborhood Playhouse School of the Theatre,[2] as well as at the Lincoln Center, and made her debut, aged 19, on Broadway in Take Her, She's Mine (December 21, 1961-December 8, 1962).

[4] Beginning in 1964 with an episode of Route 66, she began making guest appearances in several US dramatic television series of the mid-sixties, including The Doctors, The Nurses, The Trials of O'Brien, The Fugitive, A Man Called Shenandoah, and Dr. Kildare.

Also in the 1970s, Pettet guest-starred four times on the classic Rod Serling anthology series Night Gallery, appearing with her then-husband Alex Cord in the episode "Keep in Touch - We'll Think of Something".

Pettet starred in the NBC miniseries Captains and the Kings (1976), starred in the episode "You're Not Alone" from the 1977 NBC anthology series Quinn Martin's Tales of the Unexpected (known in the United Kingdom as Twist in the Tale),[5] was a guest on both Fantasy Island and The Love Boat (appearing three times on each series), and had a recurring role on Knots Landing in 1983 as Janet Baines, an LAPD homicide detective investigating the murder of singer Ciji Dunne (played by Lisa Hartman).

On 8 August 1969, Pettet had lunch at the home of actress Sharon Tate, just hours before the crimes that would be committed at that residence by members of the Manson Family.