LOS ANGELES — In the novel “Me and Earl and the Dying Girl,” written in the voice of a teenage boy, the lead character notes that “when you convert a good book into a film, stupid things happen. God only knows what would happen if you tried to convert this unstoppable barf-fest into a film. The FBI would probably have to get involved.”

Authorities of a kind did get involved, but the movie adaptation went on to win both the Grand Jury Prize and audience award when it premiered at the Sundance Film Festival this year. Adapted for the screen by the book’s author, Jesse Andrews, the film is directed with an earnest warmth by Alfonso Gomez-Rejon.

Gomez-Rejon is both a fresh voice and something of a veteran. At 42, he has been working his way up from production assistant to director over more than 20 years. Having done second-unit and television directing, he made his feature film debut with the little-seen 2014 horror film “The Town That Dreaded Sundown.” But it is with “Me and Earl” that he has fully, finally found himself.

“There is this version of everything I’ve done before, which is a very, very long story, and then there’s this,” said Gomez-Rejon in Los Angeles. “To me, even though it’s my second film it really does feel like I restarted my career, my life. I found myself as a man and a filmmaker. Everything changed with this particular film. So it is a very long story and a very short one.”

In the film, now playing in theaters, Greg Gaines (Thomas Mann) is a high school senior with a carefully cultivated anonymity that falls apart when he strikes up a friendship with Rachel Kushner (Olivia Cooke), a classmate diagnosed with terminal cancer. Greg and his best friend Earl Jackson (RJ Cyler) have long secretly done short parody remakes of classic films and they eventually set out to make a movie for real for Rachel. The film is haunted by the specter of death while moving through the joys of life.

Gomez-Rejon infuses the film with both a playful energy and a heartfelt, emotional heft. It’s a specific kind of movie, which makes use of the home video commentary track to a Powell and Pressburger movie and a clip from Les Blank’s documentary on Werner Herzog. The Gaines-Jackson movies within the movie – with titles such as “A Sockwork Orange,” “Scabface” and “Pooping Tom” – are witty and affectionate, and the film is littered with references to movies and filmmakers.

Originally from Laredo, Texas, Gomez-Rejon moved to New York for college and immediately also started working on film shoots as a production assistant. He worked as an assistant to Martin Scorsese, which created connections that led in turn to working with Nora Ephron and Robert De Niro.

“To this day, I used to be Martin Scorsese’s assistant, and that gets you some cred,” Gomez-Rejon said with a proud smile.

For a time he was back in Texas selling phones and running a coffee shop with a friend. Then he was Alejandro Gonzalez-Inarittu’s assistant on “21 Grams,” directed second unit on Ephron’s “Julie & Julia,” and Gonzalez-Inarittu’s “Babel.” Directing second unit on Ryan Murphy’s “Eat Pray Love” in turn led to directing episodes of “Glee” and “American Horror Story.”

“One thing led to another, and even though I was directing second unit on movies that got bigger and bigger and it gave me an opportunity to direct, I was still not telling my own stories,” said Gomez-Rejon.

When his father, a psychiatrist, died unexpectedly, Gomez-Rejon threw himself into more work. When he got an early copy of the script for “Me and Earl” he passionately pursued the project, making a mood-reel visual presentation to give producers an idea of what he wanted to do with the project.

“Even though this is a script written by Jesse I found a way to interpret it that felt like it was mine,” he said. “I was going to tell a personal story through this script, so it feels like I finally made a movie where I discovered my own voice while making it.”

Of his connection to the material, he added, “It felt very funny, very honest and authentic. I identified with them in the way you identify with the kids from ‘The Breakfast Club.’ There was something very beautiful about the way they all spoke.”

Besides the central trio of roles, the film has an impressive supporting cast that includes Nick Offerman and Connie Britton as Greg’s parents, Molly Shannon as Rachel’s mother and Jon Bernthal as a sympathetic teacher.

Cooke was cast before the production found its Greg, and she read against a few other potential young actors for the male lead. When she read with Mann, everyone in the room knew it was right.

“Their chemistry was perfect. It was a chemistry beyond sex or anything like that,” said Gomez-Rejon. “It maybe could go there someday but didn’t read that immediately. They respect each other. They get each other.”

The film was shot in Pittsburgh, where Andrews grew up. Though it is no longer in use, Schenley High School, where Andrews graduated from, was used as the school in the film. Greg’s family’s house is in fact the house where Andrews’ parents still live and his room was Greg’s room.

“It really did feel like a Gaines-Jackson film and your parents were next door,” said Gomez-Rejon of the production’s homey feel.

That feeling created by Gomez-Rejon spilled over to the actors as well.

“He just wanted to be in it with us, he wanted to feel everything we were feeling,” said Mann, sitting alongside Cooke and Cyler. “A lot of times he was just outside the frame, he was right there in the room with us.”

“I felt like we were the people by the end of it, we were those characters,” added Cooke.

It was at the Sundance premiere, sitting with his mother, where Gomez-Rejon first saw the film projected with the end-credits dedication to his father. The deep emotional response from audiences there was tremendous and unexpected, and the cast was caught off-guard by the waves of goodwill.

“It was good to see people get a feeling close to what it meant to us,” said Cyler, who makes his acting debut in the film. “It’s a baby of ours, and it’s great to see that people love your baby.”

Within days of finishing shooting on “Me and Earl” last summer, Gomez-Rejon was back at work on an episode of “American Horror Story.” He hasn’t been on a set since and admits he is eager to get back to shooting something soon. Building off the buzz for “Me and Earl,” there are a number of projects that could go forward as his next film.

Though he is no twentysomething Sundance kid, the experience of making “Me and Earl and the Dying Girl” marks a turning point in his career no matter what comes next. It freed him to move forward both emotionally and professionally

“I began to see myself as Greg,” said Gomez-Rejon. “You’re such a child when you lose someone and you don’t know how to handle it. Seeing his denial and his confusion and his anger, I got him. And seeing at the end that he expressed himself with a movie was the only way I thought maybe I could do something, so I would make a movie for my dad.”