Lupita Nyong’o, the level-headed breakout star of ’12 Years a Slave’

A thick, unrelenting heat permeated the Louisiana sets of “12 Years a Slave” — 100-degree-plus temperatures so intense they stifled breath. The moment a scene wrapped, cast and crew would take refuge in air-conditioned cars parked nearby. One member of the ensemble, however, stayed outdoors: Lupita Nyong’o, a 30-year-old newcomer who plays Patsey, the favorite slave of a sadistic plantation master.

“In that kind of condition, we all wanted to find even the tiniest comfort we could get,” recalled Chiwetel Ejiofor, the lead actor in the movie about a free Northerner who is abducted and sold into slavery in the South. “We were all sitting in the SUV, and she’d be standing outside, just out there in the mode of it.”

Portraying Patsey would be a harrowing challenge for even a veteran actress — the character is raped, whipped, beaten and assaulted. But Nyong’o arrived in Louisiana last summer only weeks after graduating from the Yale School of Drama, having beat out 1,000 other actresses for the part — her first feature film role ever. To prepare, the Kenya native visited Baltimore’s National Great Blacks in Wax Museum to learn more about slavery and had intense discussions about the character with director Steve McQueen.

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“Patsey didn’t have the luxury of making her situation precious, so I felt I owed it to her memory to just roll up my sleeves and do the work,” Nyong’o explained. “I wasn’t ever truly rid of Patsey. From the moment Steve called me to offer me the part to the moment we wrapped — and maybe a few weeks after that — I couldn’t sleep. The place I had to go emotionally, the intimidation of working with these actors — there was a lot going on in my head.”

Her efforts appear to have paid off. With critics heralding her turn in “12 Years a Slave” as the movie’s breakout performance, Nyong’o is already being called a lock in the supporting actress category at the Oscars.

“It’s kind of unprecedented for one of our graduates to have this much success so quickly,” said Ron Van Lieu, chair of the acting program at Yale. “It took Meryl [Streep] many more years. I think it’s a little scary.”

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If all the attention is fazing Nyong’o, she’s not showing it. In the week leading up to the film’s opening last Friday, she had, in the span of seven days, flown from New York to New Orleans to Los Angeles, attended multiple screenings and participated in more than half a dozen Q&A sessions. Despite the grueling schedule, her face showed no sign of exhaustion over lunch last week at a Beverly Hills hotel, and she carried herself like an off-duty model. Even her outfit — a simple sweater-and-shorts combination — looked like the kind of ensemble that would have her singled out by a street style photographer for a fashion magazine.

Ejiofor, a veteran actor who has been by her side throughout the promotional duties, said he has been surprised by how tranquil Nyong’o has remained amid the flurry of attention. “The first time I did a press junket, I was kind of confused,” he said. “But you sort of feel like she’s been there 1,000 times before.”

Nyong’o says she has never been particularly impressed by fame. Her father, Peter Anyang’ Nyong’o, is a prominent politician in Kenya who often made the headlines. A political science professor with a PhD from the University of Chicago, he has served as a minister of medical services and is now a member of the Kenyan parliament. But when Nyong’o was a little girl, her dad was still fighting for local democracy and would sometimes disappear for weeks at a time — in 1989, he was detained for 26 days at a government complex and held in a torture chamber.

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“I grew up in the limelight and being the child of someone famous,” she explained. “So my relationship with fame is not bedazzled.”

During her youth, Nyong’o was drawn to performing, often putting on skits with her five siblings at family gatherings. But she didn’t seriously contemplate becoming a professional actress. The people she saw on her TV set — actors on American shows like “Full House,” “The Fresh Prince of Bel-Air” and “Beverly Hills, 90210” — didn’t look like anyone she knew in Africa.

“We watched a lot of everyone else and very little of ourselves,” she said. “For that reason, it didn’t seem feasible to want to be an actor, because where the hell would I do it?”

Still, when she attended Massachusetts’ Hampshire College — where students design their own majors — she decided to focus on film and African studies. And then one summer back at home, she noticed a movie filming in her neighborhood. It was “The Constant Gardener,” the 2005 dramatic thriller based on John le Carré’s bestselling novel. Through a friend, Nyong’o landed a gig as a production assistant, at times helping actor Ralph Fiennes.

“At lunch one day, he asked me what I wanted to do, and when I told him he sighed and said, ‘Lupita, only act if there’s nothing else you want to do. It’s unforgiving,’” she remembered. “I was bummed. I realized I really had to think about why I wanted to do this, because it can be a very unstable career.”

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Yet she continued to be drawn to creative endeavors. She made a documentary, “In My Genes,” about Africans with albinism, and acted in an African MTV drama, “Shuga,” intended to raise awareness about AIDS. In 2009, she was admitted to Yale’s prestigious acting program, immediately impressing instructor Van Lieu: “She is what we call a natural,” he said, “meaning that everything she did was instinctively right.”

Nyong’o struck “12 Years a Slave” director McQueen too. After months of auditioning hundreds of young women, the filmmaker said he was beginning to get “a bit desperate and anxious” that he would never find his Patsey. When Nyong’o flew to meet him in New Orleans, he thought she might be a mirage.

“I said, ‘Oh my God, is she real?’” he remembered. And that she was a novice? “Even better. Naiveté you cannot buy. It’s underrated, because it’s what makes you fearless. That’s what she has, and she has to hold on to that innocence.”

Nyong’o, who now lives in Brooklyn, says she has been keeping a journal to track her journey through awards season. And she has been calling upon Patsey too to remind her to stay present as she travels from one red carpet to the next.

“Patsey had to be that present, because she had a volatile master whose whims could change at any time,” said Nyong’o. “In playing her, I had to employ that kind of mind-set: Just be here right now. It’s a principle I’ve valued since.”

amy.kaufman@latimes.com