She was born to Edwin Arnold Spacek and Virginia Spilman. Her paternal grandfather, Arnold A. Spacek, was the son of a Czech father, Frank J. Spacek, and a German mother, Julie Gloekner (both of whom had immigrated to Texas). Her paternal grandmother, Mary Cervenka, was also of Czech descent. Spacek's mother is of English descent.

She is a cousin of actor Rip Torn, whose mother's maiden name was Thelma Spacek.

Spacek started out in the entertainment business thanks to Torn, who was already an actor and through him she was able to enroll in Lee Strasberg's Actors Studio and then the Lee Strasberg Institute in New York City. Her first credited role was in the 1972 movie Prime Cut, in which she played a young woman sold into white slavery.

The first role that brought her notice was the 1973 film Badlands, where she met art director Jack Fisk, whom she would later marry. Their daughter Schuyler Fisk is a movie actress. Spacek is also an ardent crusader for women's rights.

Her breakout role was in Carrie, in 1976, in which she played the title character, an emotionally troubled teenager with, telekinetic powers; she was nominated for the Academy Award for Best Actress for her work in the film. She eventually won the Oscar in 1980 for Coal Miner's Daughter, in which she played country music star Loretta Lynn.

She was also nominated for a Grammy Award for her singing on that film's soundtrack album. She made a comeback of sorts in 2001 when she starred as Ruth Fowler in In the Bedroom, winning extraordinary praise and garnering the New York and Los Angeles Film Critics Awards for Best Actress. She lost the Oscar to Halle Berry that year.