NASHVILLE — K.T. Oslin, the pioneering country singer-songwriter whose biggest hits gave voice to the desires and trials of female baby boomers on the cusp of middle age, died on Monday at an assisted-living facility here. She was 78.

The country music historian Robert K. Oermann, a longtime friend, said that the cause was complications of Parkinson’s disease. He said she had also tested positive for Covid-19 last week.

“80’s Ladies,” Ms. Oslin’s breakthrough single, became an anthem for a generation of women. Released in 1987, it heralded the arrival of a songwriting voice whose sharply drawn miniatures conveyed domestic humor and pathos reminiscent of the songs of Loretta Lynn two decades earlier.

“We’ve been educated/We got liberated/And had complicating matters with men,” Ms. Oslin sang in a rich, throaty alto to open the song’s second stanza, looking back over four decades of living.

Oh, we’ve said “I do”
And we’ve signed “I don’t”
And we’ve sworn we’d never do that again.
Oh, we burned our bras
And we burned our dinners
And we burned our candles at both ends.

Its rock-leaning arrangement might have had more in common with the piano-based ballads of the California singer-songwriter Jackson Browne than with the standard Nashville fare of the era, but “80’s Ladies” was down to earth and catchy enough to make the country Top 10 in 1987. The next year, it also made Ms. Oslin the first female songwriter to earn song of the year honors from the Country Music Association.

“Do Ya,” her next single, proved that “80’s Ladies” was no fluke; rather, it was the first in a series of poignant meditations from Ms. Oslin on the ebb and flow of midlife vulnerability and desire.

“Do you still get a thrill/When ya see me coming up the hill?/Honey now do ya?” she entreats her lover, the coarse timbre in her voice redolent of some of Janis Joplin’s more intimate performances.

Do ya whisper my name
Just to bring a little comfort to ya?
Do ya?
Do ya still like the feel of my body lying next to ya?

“Do Ya” was the first of Ms. Oslin’s four No. 1 country hits, cementing her place among a distinguished circle of thoughtful, independent female songwriting contemporaries that included Pam Tillis, Gretchen Peters and Matraca Berg. In contrast to their plucky rural forebears Dolly Parton and Ms. Lynn, Ms. Oslin and her peers attended college and openly embraced feminism, weaving its insights into their lyrics.

A late bloomer, Ms. Oslin was 45 when “80’s Ladies” ignited her recording career. Before that she had worked as a folk singer, appeared in traveling productions of Broadway shows like “Hello, Dolly!” (with Carol Channing) and recorded television commercials for soft drinks and household cleaning products.

She might have languished in obscurity had Joe Galante, the longtime president of RCA Nashville, not taken a chance on her when she was at an age when many recording artists were contemplating retirement.

“I thought it was my last chance at doing anything in this business, which was all that I knew how to do,” Ms. Oslin said in a 2015 interview with Billboard. “I would have ended up selling gloves at Macy’s if it weren’t for Joe Galante. I was so naïve about the business.”

Ms. Oslin’s first two albums for RCA, “80’s Ladies” and “This Woman,” were certified platinum for sales of more than one million copies. She had 11 Top 40 country hits in all, most of them collected on the brashly titled 1993 compilation “Greatest Hits: Confessions of an Aging Sex Bomb.”

Ms. Oslin also won three Grammy Awards, as well as female vocalist of the year honors from the Country Music Association in 1988. She was later inducted into both the Texas and Nashville songwriter halls of fame.

Kay Toinette Oslin was born on May 15, 1942, in Crossett, Ark. Her father, Larry, died of leukemia when she was 5. Her mother, Kathleen (Byrd) Oslin, worked as a lab technician for the Veterans Administration.

Ms. Oslin and her brother, Larry, who died several years ago, spent much of their childhood with their mother in Mobile, Ala., and their teenage years in Houston, where Ms. Oslin studied drama at Lon Morris College and sang in a folk trio with the singer-songwriter Guy Clark.

In the mid-’60s she moved to New York, where she worked in the theater and as a jingle singer.

Ms. Oslin made New York her home for much of the next two decades, appearing in, among other productions, the Broadway musical “Promises, Promises” and the Lincoln Center revival of “West Side Story.”

She also started writing songs and was encouraged by Diane Petty, an executive with the performing rights organization SESAC, to pitch her country-leaning material to song publishers in Nashville.

She eventually was signed, as Kay T. Oslin, by Elektra Records, but neither of the singles she released for the label went anywhere. It was not until other singers started having success with her songs that her career began to gain momentum, ultimately leading to the showcase at which she performed for Mr. Galante.

Her acting experience served her well, resulting in several memorable music videos, including the “Bride of Frankenstein”-inspired staging of her final No. 1 single, “Come Next Monday” (1990).

Dusty Springfield, the Judds and the soul singer Dorothy Moore are among those who have recorded Ms. Oslin’s material. Latter-day country singers like Chely Wright and Brandy Clark have cited her as an influence.

Ms. Oslin began to focus more on acting than singing as the 1990s progressed, appearing most notably as a Nashville nightclub owner in Peter Bogdanovich’s country music-themed 1993 movie, “The Thing Called Love,” starring Sandra Bullock and River Phoenix.

She also appeared frequently on the TV talks shows of Johnny Carson, Arsenio Hall and Joan Rivers and was profiled on the ABC program “20/20.”

She had quadruple heart bypass surgery in 1995 and recorded only sporadically after that, embracing her Americana influences on “My Roots Are Showing” in 1996 and releasing a dance-floor mix of the 1951 Rosemary Clooney hit “Come On-a My House” in 2000.

No immediate family members survive.

In 2015, two years after celebrating its 25th anniversary, Ms. Oslin recorded a new version of “80’s Ladies” for her final album, “Simply.”

“That’s the one I still hear the most about, and that’s great,” she said of “80’s Ladies” in her 2015 Billboard interview. “I still love that song. It spoke to a lot of people. I don’t know how I managed to write it, but it was a great song.”