The country legend personally chose Spacek to portray her in the film, which was based on Lynn's 1976 autobiography, which traces Lynn's life, from her upbringing in Butcher Holler, Kentucky to her rise to stardom, and shares a name with her 1970 hit song.
"She was looking through a pile of pictures and when she came to one of me she said 'That's her, that's the coal miner's daughter,'" Spacek told The New York Times in 1980.
Lynn wasn't alone. Tom Rickman, who wrote the screenplay for Coal Miner's Daughter, also knew Spacek was perfect for the role.
Spacek pored over Lynn's work -- from her book to her albums. She even attended her live concerts. But perhaps the best research was meeting the "Don't Come Home A-Drinkin'" and "You Ain't Woman Enough" singer herself. Spacek says upon meeting Lynn, she knew the role -- and their friendship -- was meant to be.
"I just loved her," Spacek said. "She's so honest, and she's such a woman. She and I are the same size -- five feet two-and-one-half inches, and there is something so familiar about her. When I met her, it was like meeting a long-lost friend."
Lynn (and her band) encouraged Spacek to do her own singing and most of the songs were recorded live as she sang them.
"There's something about the way Loretta -- nobody else sings like Loretta, and nobody else talks like Loretta," Spacek told NPR's Fresh Air. "In fact, nobody in Kentucky sounds like Loretta. There's something that she does with her breath that's just unique, and once I captured her rhythm, the hardest part of Coal Miner's Daughter for me was giving it all up ... [and] not being Loretta. I was so funny when I was Loretta. She has such a great sense of humor."
Spacek's small town southern upbringing in Quitman, Texas helped her feel at home on the set.
"My father was a country agriculture agent, and my family are good country people," Spacek told The New York Times. "A far cry from Kentucky, maybe, but good honest country people are good honest country people. I felt very relaxed in Kentucky, and I got on well with the people there."
And Lynn was supportive of Spacek throughout the entire process.
"[Lynn] said 'You are me, you understand my insides.' I was so nervous when I had to sing for Michael Apted [the director] and the others, but I wasn't nervous with Loretta at all," Spacek said. "She was so sure I could do it."
Spacek took home the 1981 Academy Award for Best Actress for her performance as Lynn.
Coal Miner's Daughter was selected to be preserved in the National Film Registry in 2019.
Loretta Lynn and Sissy Spacek's Friendship
Spacek and Lynn have remained the best of friends since bonding on the set of Coal Miner's Daughter, which also starred Tommy Lee Jones as DooLittle Lynn, Beverly D'Angelo as Patsy Cline and Levon Helm as Lynn's father, Melvin "Ted" Webb.
In 2018, when Lynn was unable to attend the CMT Artists of the Year ceremony, Spacek accepted the CMT Artist of a Lifetime award on Lynn's behalf.
"From the moment we met, she's been my cheerleader, my sister and my best friend," Spacek said. "And it's like that almost 40 years later."
Sissy Spacek's Music & Career
If Spacek's natural stage presence shines through in her Oscar-winning performance as Loretta Lynn, there's a great reason. The actor, who also starred in Badlands and the Brian de Palma horror classic Carrie, originally dreamed of being a singer.
When she was 6 years old, she caught a performance by a group of school students performing in the town of Coke, Texas. Spacek told Oprah.com she was immediately taken with the Cokettes' "short satin skirts with fringes on the edge, little vests, and white cowboy hats" and began taking dance, singing and piano lessons.
After moving to New York City, she recorded commercial jingles, sang background vocals and performed at clubs.
"If I hadn't pursued acting, I could still be pounding the pavement as a musician," Spacek told Oprah.com. "But at these key moments, I listened to that voice inside me--the same one that told me, when I was a little girl sitting in the audience watching the Cokettes, that I wanted to become a performer. Everyone has an inner voice; you just have to listen to it and trust it in order to be led by it. I did that, and it gave me the ability to live a life that's true to who I am and what I really wanted."
As Spacek noted, she was able to combine her two passions when she landed the role of a lifetime.
"Even though acting wasn't what I'd originally set out to do, something told me to pursue it," Spacek said. "I'm glad I did, because it became what I love the most. The interesting thing is, years later I got to combine the two when I played Loretta Lynn in Coal Miner's Daughter."
Spacek's daughter Schuyler Fisk is also an actor and singer-songwriter. She released the album Blue Ribbon Winner in 2011.
In 2012, Spacek released her memoir My Extraordinary Ordinary Life.