In her senior year, George Lucas shot American Graffiti at her high school gym and Fred Roos asked her to read for a small part.

She was primarily a gymnast and 1, 3, and 5 meter diver in her school years, which led to her being cast as a stunt double for Trish Van Devere's triumphant dive at the end of the movie One is a Lonely Number.

Quinlan had an uncredited role in 1972's One Is a Lonely Number[7][10] but her official credited film debut was in George Lucas's 1973 movie American Graffiti, at the age of nineteen.

[9] Quinlan also appeared in feature films like Lifeguard (1976), Airport '77 (1977), The Promise (1979), The Runner Stumbles (1979), Sunday Lovers (1980), Twilight Zone: The Movie (1983), Sunset (1988), Clara's Heart (1988), and Trial by Jury (1994).

In 1997, she appeared in Event Horizon (1997) and won a Blockbuster Entertainment Award as Favorite Supporting Actress-Suspense for Breakdown (1997), playing Kurt Russell's character's kidnapped wife.