Quinlan was born in Pasadena, California, the daughter of Josephine (née Zachry), a military supply supervisor, and Robert Quinlan, a television sports director. She was raised in Mill Valley, California, where she attended Tamalpais High School, studied drama, and began her acting career. She has been married to actor Bruce Abbott since April 12, 1994. They have a son, Tyler (born 1990).
Quinlan made her film debut in George Lucas's 1973 nostalgic look at the early '60s, American Graffiti, at the age of 19 (although she did appear in an uncredited role in 1972's One Is a Lonely Number). As a young actress, she guest-starred in several 1970s television series, including Police Woman, Ironside, Emergency!, Kojak, and The Waltons. She has appeared in over 50 films but is perhaps best known for her roles as sixteen-year-old schizophrenic Deborah in the film version of I Never Promised You a Rose Garden, for which she earned a Best Actress in a Motion Picture-Drama Golden Globe nomination, and as an astronaut's wife, Marilyn Lovell, in the 1995 true story Apollo 13 opposite Tom Hanks, for which she earned a Best Supporting Actress – Motion Picture Golden Globe nomination and a Best Supporting Actress Academy Award nomination. Quinlan also made a mark as Jim Morrison's Celtic pagan lover Patricia Kennealy in Oliver Stone's The Doors and won a Blockbuster Entertainment Award as Favorite Supporting Actress-Suspense for Breakdown (1997) with Kurt Russell. Her recent work includes the TV series House, the 2006 remake of the horror classic The Hills Have Eyes, the wife of a government traitor in the 2007 film Breach, the mother of the two brothers in the Fox drama Prison Break, and a senator in "Alliances", a 2011 episode of the science-fiction series Stargate Universe.