native of Fort Worth, Texas, Buckley is known for the 1977–81 TV dramedy Eight Is Enough. She joined the show in its second season when the original star, Diana Hyland, died after the first four episodes of season one, and her character Joan Bradford died as well. Buckley was cast as the widower's new romantic interest, Sandra Sue "Abby" Abbott, who became stepmother of the eight children to which the series' title refers.
Buckley appeared in the original movie version of Carrie in 1976, playing Miss Collins, Carrie's gym teacher. In 1977, she recorded an uncredited solo on the song "Walking in Space", in the movie Hair.
On television, she received two Daytime Emmy Award nominations for Outstanding Performer in a Children's Program/Special, for NBC Special Treat - Bobby and Sarah (1984) and ABC Afterschool Special - Taking a Stand (1989).
Her screen roles during the 1980s include Bruce Beresford's film Tender Mercies, where she played a country music singer and sang the Academy Award-nominated song "Over You". She also appeared in the Woody Allen film Another Woman (1988), Roman Polanski's Frantic (1988), Lawrence's Kasden's Wyatt Earp (1994).
From 2001 to 2003, she played the role of Suzanne Fitzgerald in seasons 4–6 of the HBO series Oz.
She also has guest-starred in a number of television series, including Without a Trace, Law & Order: Special Victims Unit, and Monk. She guest-starred in a Christmas special of the TV series Remember WENN, created and written by Rupert Holmes for the cable channel American Movie Classics, in which she sang two Holmes original songs: "Christmas is Waiting", and "You Make It Christmas". She appeared as Marion Leckie, mother of Robert Leckie in the HBO series The Pacific, which aired in 2010.
Also in 2010, she appeared in the 18th episode of Melrose Place as a food critic cast by her brother Norman Buckley, who directed the episode. She also guest-starred in an episode of the Fox series The Chicago Code. She was a recurring guest star on Pretty Little Liars as Regina Marin, also directed by her brother Norman. In 2008, Buckley played Mrs. Jones in M. Night Shyamalan's The Happening. In 2017, Buckley was one of the stars of M. Night Shyamalan's Split, the number-one film at the box office for three weeks.
Her other television credits include guest-starring as Meg's mother in The Leftovers on November 30, 2015, appearing in five episodes of the 2017-2021 series Supergirl. Buckley was also cast in season three of the series Preacher in 2018.
