Naomi Judd, who as one half of the mother-daughter duo the Judds dominated the country music charts in the 1980s with a blend of tight vocal harmonies, traditional arrangements and modern pop aesthetics, died on Saturday outside Nashville. She was 76.

Ashley Judd, the actress, confirmed her mother’s death on Twitter. She did not specify where she died or the cause but said, “We lost our beautiful mother to the disease of mental illness.” Naomi Judd had lived for years on a farm in the hills above Franklin, Tenn., a suburb of Nashville.

With her other daughter, Wynonna, Ms. Judd rocketed to country stardom in 1983 with the single “Had a Dream (for the Heart)” and, a year later, with the duo’s chart-topping first album, “Why Not Me.”

More hits followed — including 14 No. 1 songs — and a long list of honors, including nine Country Music Association Awards and five Grammys.

The Judds were a leading force in the New Traditionalist movement in country music, a reaction against the glitz and glamour of the Urban Cowboy sound and in favor of roots-oriented instrumentation and vocals.

Though they were not in the vanguard — musicians like George Strait and Ricky Skaggs had been performing for years when the Judds emerged — the duo stood out as a family band, a once-common arrangement in country music that had fallen out of favor.

In their songs and especially in Naomi’s life story as a struggling single mother, they spoke to millions of working-class women in the South and beyond, with songs about adult heartbreak, the solitude of family life and the breakdown of community in modern society.

In one of their many hits, “Grandpa (Tell Me ’Bout the Good Old Days)” (1986), they sang:

Was a promise really something people kept

Not just something they would say

Did families really bow their heads to pray?

Did daddies really never go away?

Oh, Grandpa, tell me ’bout the good old days

They released six albums, most of them laden with hit songs. The Judds were at the time the most successful country duo in history, with more than 20 million albums sold.

They made for a compelling stage act. Naomi was more telegenic and engaging with crowds, while Wynonna was more reserved but a better singer. With matching bright red hair and just 17 years between them in age, they were often mistaken for sisters and played up their resemblance onstage and at awards shows — they once arrived at a ceremony in matching Scarlett O’Hara outfits.

But their run was brief: Naomi announced in 1990 that she had a life-threatening case of hepatitis C, and they played their last concert in 1991.

Doctors had given Naomi three years to live, but in 1995 her disease was in full remission. By then Wynonna had set off on a successful solo career, and Naomi turned to activism, acting and writing.

The Judds reunited for the occasional concert or brief tour, and recently announced another tour to start this fall. Last month, at the CMT Music Awards, they performed together on television for the first time in years. They were to be inducted into the Country Music Hall of Fame on Sunday night.

Diana Ellen Judd was born on Jan. 11, 1946, in Ashland, a coal-mining town in northeastern Kentucky, along the Ohio River. Her father, Charles Glen Judd, owned a gas station, and her mother, Pauline Ruth (Oliver) Judd, was a homemaker.

When she was 3, an uncle molested her, an experience she later cited as the root of her struggles with anxiety and depression.

Naomi was an honors student with plans for college. But a brief romance with a high school football player left her pregnant at 17, and when the father skipped town, she married another suitor, Michael Ciminella. Wynonna was born the week Naomi graduated in 1964.

The family moved to Los Angeles in 1968, where Mr. Ciminella found work, and Ms. Judd studied for a nursing degree. Ashley was born that same year. But Ms. Judd said the marriage never clicked, and they divorced in 1972.

Single and raising two daughters, Ms. Judd left school and worked as a model, waitress and secretary, including for the band Fifth Dimension. She dated occasionally, but when one casual boyfriend beat and raped her, she fled California, moving to Morrill, Ky., a town in the center of the state with one road and 50 residents.

They lived simply, without a TV or phone. Ms. Judd studied nursing in nearby Berea. To entertain herself, Wynonna began singing and playing guitar. Occasionally, Ms. Judd would join in, and soon they were regularly making music together.

“I could only afford the used record bin, and there was a 33-1/3 album of Hazel and Alice — Hazel Dickens and Alice Gerrard,” she told the documentary filmmaker Ken Burns. “They were all coal-mining songs. And as these women harmonized together, it came to me: Wynonna and I couldn’t talk to each other, but, lo and behold, we could sing together.”

They decided to give Nashville a shot, and they moved to Music City, U.S.A., in 1979, where Ms. Judd found a job as a nurse. Again, the three of them scraped by, sharing a single motel bed and living on bologna sandwiches, recording demo tapes in their free time and hoping for a break.

It finally came in 1983, when one of Ms. Judd’s patients turned out to be the daughter of an executive at RCA Records. They got an audition, and, that same day, they signed a contract. A few months later, “Had a Dream (for the Heart)” was released, climbing to No. 20 on the country charts.

“Suddenly, we had a future,” she told The Wall Street Journal. “For the first time in my life, I felt alive.”

The Judds’ hits included “Mama He’s Crazy,” “Why Not Me,” (both in 1984); “Girls Night Out” (1985); “Rockin’ With the Rhythm of the Rain” and “Grandpa (Tell Me ’Bout the Good Old Days” (both in 1986); “Turn It Loose” (1988); and “Love Can Build a Bridge” (1990).

Along with her daughters, Ms. Judd is survived by her husband, Larry Strickland, who was a backup singer for Elvis Presley.

After the duo broke up and Ms. Judd recovered from her hepatitis, she pursued acting, with guest appearances on sitcoms like “Third Rock from the Sun” and roles in made-for-TV movies like “Rio Diablo” (1993), starring Kenny Rogers. She was a judge on “Star Search” in 2003 and 2004, and she hosted a talk show, “Naomi’s New Morning,” for two seasons in the mid-2000s. She later had a radio talk show on SiriusXM.

Ms. Judd also became increasingly vocal about her struggles with mental illness, especially after a series of reunion shows in 2009 and 2010.

“I would come home and not leave the house for three weeks, and not get out of my pajamas, and not practice normal hygiene,” she said on Good Morning America in 2016. “It was really bad.”

She recounted that struggle in her 2016 memoir, “River of Time: My Descent into Depression and How I Emerged with Hope.”

In it, she described “two and a half years of my life, during which I went through the hell of mental illness,” but also “rising again to be thankful for taking my next breath, for the gift of a clear thought, for wresting from a nightmare a way to find joy in each day.”

That newfound joy was evident in the planning for the duo’s upcoming tour. In a news release this month, Ms. Judd said she was looking forward to reconnecting with fans and singing with her daughter Wynonna.

Referring to Wynonna, Ms. Judd said: “She asked me if I was still going to twist, twirl and crack jokes. I answered, ‘Heck yeah! I’m too old to grow up now!’”

Isabella Grullón Paz contributed reporting.