Jamie Barton has an obvious affinity for strong, confident and outspoken women — both on and off the operatic stage. Perhaps that’s because, well, she’s one herself.

The extravagantly gifted American mezzo-soprano has made memorable recent appearances at the San Francisco Opera as Fricka, the imperious queen of the gods inWagner’s “Ring” Cycle, and just last month as the witch Jezibaba inDvorák’s “Rusalka.”Now Barton is poised to take on a figure who stands (in some circles at least) as the embodiment of fearless female indomitability: Supreme Court Justice Ruth Bader Ginsburg.

“When There Are Nine,” which has its world premiere on Friday, Aug. 2, at the Cabrillo Festival of Contemporary Music in Santa Cruz, is a choral song cycle built around Ginsburg’s life and career. Commissioned by the festival from Michigan composer Kristin Kuster (with a libretto by poet Megan Levad), the piece grew originally out of Barton’s horror at the 2016 release of the “Access Hollywood” tape, with then-candidate Donald Trump’s remarks about grabbing women by their genitals.

“That was a moment that was very disturbing to me, and to a lot of people,” Barton said during a recent interview. “I got on Facebook and wrote a small novel about what it would mean if someone like this were elected.”

One of the people who saw that and responded was conductor Cristian Macelaru, the music director of the festival.

”他说,“我觉得一样强烈。我们ve got to do something.’ So he proposed that the festival should commission something that would make a strong statement in a good direction. And celebrating RBG — who’s a big fan of classical music — seemed like the way to push back against something so hateful and so awful.”

For Barton, 37, blending her musical activities with frankly stated positions on social and political issues has become an increasingly notable trademark. On social media, where she maintains a lively presence, she’s been a forthright advocate on queer issues (she identifies as bisexual). She’s spoken out on matters of weight and body positivity, most recently in aTwitter threadon the dangers of dieting.

Some of that urgency has found its way into her programming. In September, Barton will headline the prestigious closing night of the BBC Proms series in London, and she promises to give it a queer-friendly ethos.

And in December, when she and pianist Kathleen Kelly return to the Bay Area for arecitalsponsored by San Francisco Performances, it will be with a program celebrating women.

“I take the opportunity to do a little bit of gender bending,” she says. “There’s a group of songs by female composers – Nadia and Lili Boulanger, Amy Beach, Elinor Remick Warren – and then at the end of the recital, there are songs written by men for men to sing, which I present as a bisexual woman.

“I’m taking that moment to say, ‘I experience these things, and I have these feelings.’ Because I think it’s more of a human experience than a strictly gendered experience.”

Barton grew up in the rural reaches of northern Georgia, on land that had been in the Barton family for generations. Although her immediate family has always been a little different from their neighbors – Democrats, for one thing, in a ruby-red political district – she describes her background as solidly blue-collar.

“My dad worked in factories for years, but he’s now in his dream job as the personal auto mechanic to a guy who owns a fleet of vintage cars. My dad is an expert on electrical systems and A-models, so if you need an air conditioning system put into a ’48 Willys, he’s your guy.”

Music was a regular feature in their home — but almost exclusively rock and bluegrass, which she discovered both through recordings and in the massive “pickin’ and grinnin’ ” get-togethers that her great-aunt and great-uncle hosted, in which anyone with an instrument would bring it and join in.

Her taste for classical music, Barton says, developed as a form of teenage rebellion after she stumbled onto a compilation CD of Romantic piano music with the improbable title “Chopin and Champagne.” That passion for music guided her to Shorter College, a Baptist school in her hometown of Rome that happened to have a first-rate vocal department.

“The faculty there was just astounding. There were people who’d been on the staff for 55 years, and these people were true geniuses. The students, we’d go to competitions, a bunch of us from Shorter, and we’d just take everything.”

Barton went on to do graduate work at Indiana University, and from there on her career ascent was swift. She won the Cardiff Singer of the World competition in 2013, followed two years later by the Richard Tucker Award. In addition to her acclaimed appearances as Fricka and last year in Donizetti’s “Roberto Devereux,” she recently appeared for the first time as Sister Helen Prejean in Jake Heggie’s “Dead Man Walking,” and she’s about to add the daunting role of Amneris in Verdi’s “Aida” to her repertoire.

All of which, as she admits, can take its toll in time and energy. She lives in Atlanta (“well, strictly speaking, I keep my stuff in Atlanta”); she has a boyfriend in Seattle, a massage therapist who understands the demands of the career she’s chosen; and she travels constantly.

“I wouldn’t mind finding a little more balance between life and career. I have what I call the rule of three when I’m looking at gigs, and an offer has to satisfy at least two of these three or it’s off the list.

“这是一个地方我想去,卡内基Hall or San Francisco or something like that. It has to be a project that I am really interested in. Or it has to payallof the money.”

In the meantime, Barton has her eye on some dream projects. She still hopes to get mandolinist and composer Chris Thile to write some music for her, and to accompany her in a program that also includes the lute songs of the Renaissance Englishman John Dowland.

And she wants to sing Carmen.

“I’d like to do something that celebrates people of all different shapes, sizes, colors — and I think that is who Carmen and her people are. Whereas Don José is leading a very conservative, very Birmingham, Ala., kind of existence.

“Now, I come from that world. I understand it. But also I am of the more colorful liberal world now, so I’ve got a specific understanding of who that character is — and quite honestly I think I could sing the snot out of it.”

Cabrillo Festival of Contemporary Music:8 p.m. Friday, Aug. 2, through Aug. 11. $20-$65. Santa Cruz Civic Auditorium, 307 Church St., Santa Cruz. 831-420-5260.www.cabrillomusic.org